Autism Spectrum Disorder in Adults: Why Getting the Right Diagnosis Matters

Table of Contents

• Key Points
• Why More Adults Are Seeking an Autism Diagnosis
• The Problem of Misdiagnosis in Adults with Autism
• Why an Accurate Diagnosis Matters
• How This Review Was Conducted
• The DSM-5 Diagnostic Criteria for Autism
• Diagnostic Tools for Adults with Suspected Autism
• Clinical Implications
• Limitations of This Review
• Recommendations for Patients
• Frequently Asked Questions
• Source Information

Key Points

• About 1 in 4 adults with autism report at least one previous psychiatric diagnosis they believed was a misdiagnosis.
• 70–80% of adults with autism meet criteria for at least one other psychiatric condition, such as anxiety, depression, ADHD, or OCD.
• In a review of 93 adults, the ADOS-2 Module 4 had sensitivity 0.65 and specificity 0.76, missing about 35% of autistic adults.
• One study found the AQ had specificity 0.29, incorrectly flagging nearly three-quarters of non-autistic adults.
• In one study, women with autism reported perceived misdiagnosis more often than men (31.7% vs. 16.7%).

Why More Adults Are Seeking an Autism Diagnosis

The number of adults seeking a first-time autism diagnosis has risen sharply, and several trends explain why. Autism spectrum disorder (ASD) is a neurodevelopmental condition that causes pervasive difficulties with social communication, along with restricted, repetitive interests and behaviors that begin early in childhood.

A major turning point came with the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), published in 2013. The DSM-5 combined three separate diagnoses — autistic disorder, Asperger's syndrome (AS), and pervasive developmental disorder-not otherwise specified (PDD-NOS) — into one autism spectrum. It also, for the first time, explicitly allowed an autism diagnosis to be made in adolescence or adulthood, acknowledging that many people were missed in childhood.

That missed-diagnosis problem is real, even in older adults. Recent research has found that a diagnosis can be missed in patients well over 50 years old, who were likely underdiagnosed because they grew up in an era when autism was not as well recognized.

Why do symptoms sometimes stay hidden for decades? The DSM-5 notes that symptoms may not become apparent until later life, when social communication demands exceed a person's capacity to cope. Many adults notice difficulties during major life transitions such as:

• Moving or graduating
• Starting a new job
• Managing finances and adult responsibilities
• Maintaining relationships and building social networks

Other undiagnosed adults grew up in environments that happened to accommodate their social needs and repetitive behavior patterns. People with "high-functioning autism" (autism without intellectual disability, defined as an IQ of 70 or above) are especially likely to be diagnosed late, just as individuals with Asperger's syndrome often were. Asperger's syndrome was added to the DSM-IV in 1994, but research found no distinct developmental trajectory separating it from autism, so it was folded into the autism spectrum in the DSM-5 — although debates about its removal continue.

Social media has also played a significant role in the rising number of adults questioning whether they might be on the autism spectrum. The #Autism hashtag on TikTok had garnered 11.5 billion views as of a study collecting data before 2022. A separate study found it was the ninth most-viewed health-related hashtag on TikTok as of 2021.

However, social media is an unreliable teacher. An analysis of popular ASD-related videos found that only 27% were accurate while 73% were inaccurate or overgeneralized. Healthcare professionals often provide accurate information, but misinformation can still lead to inappropriate self-diagnosis and wasted time, stress, and money spent trying to validate a diagnosis. Interestingly, a 2023 study using machine learning to analyze social media posts found that features like idiosyncratic interests and linguistic patterns could identify autistic users with precision and recall rates of 85% and 82% respectively — suggesting that online behavior may someday help flag adults who deserve a formal evaluation.

The Problem of Misdiagnosis in Adults with Autism

Many adults with undiagnosed high-functioning autism develop strategies to hide their autistic traits, a process known as masking or camouflaging. This makes accurate diagnosis even harder, because the person sitting in front of the clinician may not display obvious signs.

The National Institute for Health and Care Excellence (NICE) guidelines warn that high-functioning autism can be misdiagnosed as a broad range of psychiatric conditions, including personality disorder, anxiety or mood disorder, or a psychotic illness. One key reason for this confusion is timing: most psychiatric conditions like anxiety, depression, and personality disorders typically begin in adolescence or adulthood, while autism — by definition — begins in the developmental period. Clinicians who treat adults and who did not receive formal training on autism and other developmental conditions may simply not consider childhood-onset disorders when evaluating an adult.

Accurate diagnosis is further complicated by high rates of co-occurring conditions. It is estimated that 70–80% of adults with autism meet diagnostic criteria for at least one other psychiatric condition. The most common co-occurring conditions include:

• Anxiety disorders
• Depression
• Attention-deficit/hyperactivity disorder (ADHD)
• Obsessive-compulsive disorder (OCD)

This overlap can make it genuinely difficult to determine whether symptoms are due to autism itself or a combination of separate conditions.

The consequences of misdiagnosis are serious. About 1 in 4 adults with autism (25%) report at least one previous instance in which they received a psychiatric diagnosis they believed to be a misdiagnosis. In a study of misdiagnosis in autistic adults, the most frequently reported perceived misdiagnoses were:

• Personality disorders: 12.3%
• Anxiety disorders: 6.6%
• Mood disorders: 6.2%
• Chronic fatigue syndrome/burnout-related disorders: 4%
• ADHD: 2.8%

A striking gender gap also emerged in this research. Women with autism were more likely than men to report perceived misdiagnoses (31.7% vs. 16.7%) and had a higher frequency of prior psychiatric diagnoses (65.8% vs. 34.2%). This distinct pattern highlights the need for a more diligent, nuanced diagnostic approach for women presenting with psychiatric concerns.

Misdiagnosis can harm a person's sense of identity and delay access to interventions and accommodations. Research consistently shows that autistic adults who were diagnosed later in life describe a negative impact on their wellbeing due to years of unexplained challenges with social interaction, sensory processing, and flexibility.

Why an Accurate Diagnosis Matters

A correct autism diagnosis in adulthood brings both tangible and intangible benefits. Practically, a formal diagnosis can help a person gain access to accommodations at school or in the workplace, such as individualized job or academic coaching and flexible scheduling.

Equally important is the psychological benefit. A diagnosis in adulthood can lead to a deeper sense of identity after years of feeling isolated because of unrecognized autistic traits. Many late-diagnosed adults describe relief at finally having an explanation for lifelong difficulties with social interaction, sensory processing, and adapting to change.

How This Review Was Conducted

The authors performed a systematic literature search using PubMed, PsycINFO, and Google Scholar to identify relevant recommendations, diagnostic tools, and common differential diagnoses for adults with autism. Search keywords included "adult autism diagnosis," "late-diagnosed ASD," "autism spectrum disorder in adulthood," and "differential diagnosis of ASD."

Studies published within the last two decades were prioritized to ensure relevance, though foundational research was also included. Inclusion criteria covered peer-reviewed articles and book chapters that examined diagnostic criteria, misdiagnosis, psychiatric comorbidities, and the lived experiences of adults diagnosed with autism later in life. Articles were screened by title and abstract, and full-text reviews were conducted to assess methodological quality. References from key studies were also reviewed to identify further relevant literature.

The DSM-5 Diagnostic Criteria for Autism

There is no single medical test for autism, just as there is no single test for most psychiatric disorders. Instead, diagnosis relies on the DSM-5 criteria, which require symptoms in two core domains plus evidence of functional impairment.

Social Deficits and Communication Impairment

Social deficits in autistic adults often show up as a profound lack of intuitive understanding of interpersonal relationships. This can lead to social isolation, eccentric or self-centered interactions, and significant challenges with empathy and reading social situations.

Even autistic adults with advanced language skills may struggle to understand and use nonverbal communication — facial expressions, body language, and gestures — resulting in a formal, rigid communication style. Social-pragmatic language deficits (difficulty with the practical use of language in social contexts) further complicate interactions. Autistic individuals may struggle with context, interpreting figurative language like idioms or sarcasm, and engaging in the back-and-forth of conversation. These difficulties create real barriers in everyday life, leading to frequent misunderstandings in both personal and professional settings.

Restricted, Repetitive Thoughts and Behaviors

Repetitive thoughts and behaviors come in several forms, and distinguishing them is essential when evaluating an adult for autism. Types of repetitive thoughts include preoccupations, obsessions, ruminations, delusions, and overvalued ideas.

Preoccupations — pleasurable, intense interests in specific topics — are the most common type of repetitive thought in autism. While generally enjoyable, they can become problematic when excessive or overly time-consuming. For example, an autistic adult might spend so much time thinking about a favorite topic that they become distracted from activities of daily living (ADLs).

Repetitive behaviors offer a more observable source of diagnostic information. There are five types to consider:

1. Stereotypies — repetitive, voluntary, non-purposeful movements or utterances, such as hand flapping, body rocking, and toe walking
2. Tics — sudden, rapid, recurrent movements or sounds
3. Compulsions — repetitive behaviors performed according to rules, often to reduce anxiety
4. Extrapyramidal symptoms (EPS) — medication-induced or neurological movement abnormalities
5. Automatisms — automatic, unconscious behaviors

In autistic adults without intellectual disability, stereotypies are the most common form of repetitive behavior, although the others can also appear. Stereotypies often involve bilateral movements of the upper extremities and can help alleviate strong emotions such as irritability, anxiety, anger, or excitement — feelings that contrast with the person's baseline mood. Importantly, stereotypies also occur in other conditions, including autism with intellectual disability, severe mood dysregulation, catatonia, and schizophrenia, making them a crucial clue — but not proof — in the diagnostic process.

Clinically Significant Impairment in Functioning

The third core criterion is that symptoms must cause clinically significant impairment in social, occupational, or other important areas of functioning. In adults, this often means difficulty forming and maintaining relationships, trouble interpreting social cues, or challenges initiating conversations.

Occupationally, autistic adults may struggle to adapt to changes in routine, manage sensory sensitivities, or understand workplace hierarchies — all of which can hinder job performance and career advancement. Daily functioning can also suffer, with difficulties organizing tasks, managing time, or coping with the unpredictability of everyday life. These impairments are substantial barriers to quality of life and independence, which is why evaluating functional limitations is a vital part of the diagnostic process.

Diagnostic Tools for Adults with Suspected Autism

Evaluation of an adult with suspected autism should be performed by trained, competent professionals through a multistep, multidisciplinary assessment that considers current and past behavior as well as early development. Expert clinicians — those with extensive exposure to autistic individuals — show better interrater reliability when they rely on their own experience and knowledge rather than a standardized symptom checklist. For less experienced clinicians, however, using the latest DSM criteria provides superior structure and significantly enhances diagnostic reliability.

In complex adult assessments, clinical judgment can be supported by standardized instruments. These fall into three categories:

• Self-report tools — questionnaires about current behaviors or feelings
• Observation-based assessments — clinicians watch and rate real-time behavior
• Informant-based evaluations — a parent, sibling, or close individual reports on current and childhood behaviors

Informant-based instruments like the Autism Diagnostic Interview-Revised (ADI-R) and the Diagnostic Interview for Social and Communication Disorders (DISCO) are thorough but impractical for many adults who no longer have a caregiver to report on their behalf. They are also costly and time-intensive — the ADI-R takes about 1.5 hours and the DISCO can take up to 3 hours — and they may lack sensitivity for adult populations.

Autism Diagnostic Observation Schedule-2 (ADOS-2)

The ADOS-2 is widely regarded as a key diagnostic tool. It uses semi-structured observation with modules tailored to different developmental and language levels. While it is reliable and valid in children, Module 4 — designed for fluent adolescents and adults — has undergone fewer psychometric evaluations.

Studies show the ADOS-2 Module 4 can distinguish autism from psychopathy and from neurotypical adults, but it struggles to differentiate autism from schizophrenia. Recent algorithm revisions improved sensitivity and specificity, especially in high-functioning individuals. However, a review of 93 adults found it only moderately effective at predicting autism diagnoses, with a sensitivity of 0.65 and specificity of 0.76 — meaning it missed about 35% of autistic adults and incorrectly flagged about 24% of non-autistic adults. Its lengthy administration time and specialized certification requirements also limit its practical use in adult assessments.

Autism-Spectrum Quotient (AQ)

The AQ is a self-report screening tool for autism traits in adults with normal intelligence. It has relatively good sensitivity and specificity across the lifespan, but it cannot reliably predict autism in adults without intellectual disability and may produce false positives, particularly in people with ADHD or anxiety disorders.

Studies have found low specificity in clinical settings. One study reported a sensitivity of 0.77 and specificity of 0.29 — meaning that while it caught most autistic adults, it also incorrectly flagged nearly three-quarters of non-autistic adults. That level of false positives seriously limits its usefulness for triaging referrals. Still, clinicians can use discrepancies between self-reports and clinical observations to uncover camouflaging or over-reporting of symptoms. Overall, the AQ sum score serves best as an index of autistic traits rather than a diagnostic or triage tool.

Developmental, Dimensional and Diagnostic Interview — Adult Version (3Di-Adult)

The 3Di-Adult is a promising, time-efficient diagnostic interview. In a preliminary 2018 investigation of its psychometric properties, it showed high sensitivity (95%) and specificity (92%) in its ability to discern autism cases — even when the comparison group included individuals with other psychiatric conditions. Its feasibility and psychometric properties suggest it is a valid, reliable tool for diagnosing autism in adults based on DSM-5 criteria.

Ritvo Autism Asperger Diagnostic Scale-Revised (RAADS-R)

The RAADS-R is a modified version of the original Ritvo Autism Asperger Scale, first published in 2008, and was designed to address a major gap in screening services for autistic adults. An international validation study from 2011 found the RAADS-R to be highly accurate, with sensitivity of 97% and specificity of 100% in distinguishing autistic adults from those without psychiatric conditions and from those with other psychiatric diagnoses.

Unfortunately, more recent studies have not replicated these results. In two separate studies from 2019 to 2021, researchers found that the RAADS-R lacks predictive validity and is not an appropriate screening tool for adults with a question of autism. This striking discrepancy underscores how much more research is needed to identify reliable screening tools for this population.

Adult Repetitive Behavior Questionnaire-2 (RBQ-2A)

The RBQ-2A is an 80-item self-report questionnaire that assesses repetitive motor behaviors, sensory interests, insistence on sameness, and restricted interests. Although relatively new, studies suggest it reliably measures restricted and repetitive behaviors in autistic adults, with autistic adults scoring higher than IQ-matched neurotypical adults, and with strong internal consistency.

A 2023 study supports its use for assessing specific behaviors or screening for autism. It was designed specifically for adults and can be used with both autistic and neurotypical populations. However, its reliance on self-reporting means it is only suitable for individuals capable of completing the questionnaire independently.

Social Responsiveness Scale (SRS)

Like most autism assessment tools, the SRS was originally developed for children as a measure of social impairment in autism, but it has shown promising reliability in adults as well. Studies confirm its validity in measuring social difficulties, with strong internal consistency and sensitivity in distinguishing autistic from neurotypical adults.

Importantly, informant-based versions are more reliable than self-reports, which can be influenced by the person's level of self-awareness. While effective, the SRS is best used alongside other diagnostic tools and clinical observations for a comprehensive evaluation.

Social Communication Questionnaire (SCQ)

The SCQ is another questionnaire-based tool used in autism assessment. It is noted in the review as a common instrument, though the published text provided for this article was truncated before full details of its adult validation could be described.

Clinical Implications

A careful differential diagnosis — the process of systematically ruling out other conditions — is essential for adults who present with a question of autism. Clinicians must evaluate the subtle differences in symptoms and behaviors while obtaining a robust developmental history to accurately identify whether autism, another psychiatric disorder, or both are present.

Because 70–80% of autistic adults have at least one co-occurring psychiatric condition, the clinical reality is that many patients will need treatment for both autism and conditions like anxiety, depression, ADHD, or OCD. Getting the diagnostic picture right is not just an academic exercise; it determines which treatments will help and which may be unproductive or even harmful.

The review also highlights a pressing need for updated clinician training. Many adult-focused mental health professionals have not received formal education on autism and other developmental conditions, which contributes directly to missed and incorrect diagnoses. Large-scale research remains paramount for refining adult autism diagnosis, particularly for underdiagnosed groups like women and older adults.

Limitations of This Review

The authors acknowledge several factors that complicate both clinical diagnosis and the research itself. Existing diagnostic tools frequently miss subtle or atypical presentations, especially in underdiagnosed groups such as women, older adults, and people without intellectual disability.

Many standardized instruments were developed and validated primarily in children; their psychometric properties in adults are less well established. The ADOS-2, for example, has limited adult-focused evaluations, and the RAADS-R's dramatically different results between the 2011 validation study and the 2019–2021 studies demonstrate how fragile our current tools are.

Access to informant-based assessments is often impossible for adults whose parents have died, are unavailable, or do not remember details of early childhood. The lack of pediatric records further compounds this difficulty. And because autism symptoms must be present in early childhood by definition, clinicians must sometimes rely on current symptoms meeting diagnostic criteria when no evidence of childhood history can be obtained.

Recommendations for Patients

If you are an adult wondering whether you might be autistic, this review offers several practical takeaways:

1. Seek a clinician with specific autism expertise. Expert clinicians with extensive exposure to autistic adults tend to make more reliable diagnoses than those relying solely on checklists.
2. Bring your developmental history. Any information about your childhood — report cards, family recollections, school evaluations — can be invaluable, since autism must have been present in early development.
3. Expect a thorough, multidisciplinary evaluation. A proper assessment considers current and past behavior, early development, and functional impairment across social, occupational, and daily living domains.
4. Be aware that screening tools have limits. A high score on an online autism quiz is not a diagnosis. Tools like the AQ and RAADS-R have significant false-positive rates, and even well-regarded measures like the ADOS-2 are imperfect in adults.
5. Discuss co-occurring conditions. Anxiety, depression, ADHD, and OCD are common in autistic adults. A complete evaluation should address all of these, not just autism alone.
6. If you are a woman, be prepared to advocate for yourself. Research shows women are nearly twice as likely as men to report having been misdiagnosed, and they carry a higher burden of prior psychiatric diagnoses.
7. Treat social media as a starting point, not a source of truth. Only about 27% of popular autism videos are accurate. Use credible medical sources and professional evaluation to validate your concerns.

These recommendations come from the peer-reviewed literature reviewed in this article, and they reflect the authors' expert opinion on current best practices for adult autism diagnosis.

Frequently Asked Questions

Why are more adults now seeking a first-time autism diagnosis?

The DSM-5, published in 2013, combined three separate diagnoses into one autism spectrum and explicitly allowed diagnosis in adolescence or adulthood. Symptoms may become apparent when social demands exceed coping capacity, often during life transitions like moving, starting a job, or managing finances. Social media has also prompted more adults to question whether they are autistic.

How common is misdiagnosis among adults with autism?

About 1 in 4 adults with autism report at least one previous psychiatric diagnosis they believed was a misdiagnosis. In one study, the most frequently reported perceived misdiagnoses were personality disorders (12.3%), anxiety disorders (6.6%), mood disorders (6.2%), chronic fatigue or burnout-related disorders (4%), and ADHD (2.8%). Women reported misdiagnosis more often than men.

What conditions are most often confused with autism in adults?

High-functioning autism can be misdiagnosed as personality disorder, anxiety or mood disorder, or a psychotic illness, according to NICE guidelines. The confusion arises partly because most psychiatric conditions begin in adolescence or adulthood, while autism begins in the developmental period. Co-occurring anxiety, depression, ADHD, and OCD are also common and can complicate diagnosis.

What does the ADOS-2 sensitivity and specificity mean for adults?

In a review of 93 adults, the ADOS-2 Module 4 had a sensitivity of 0.65 and specificity of 0.76. This means it missed about 35% of autistic adults and incorrectly flagged about 24% of non-autistic adults. It also struggles to differentiate autism from schizophrenia. Its lengthy administration and certification requirements limit practical use in adult assessments.

Can a high score on an online autism quiz diagnose autism?

No. A high score on an online autism quiz is not a diagnosis. Tools like the AQ and RAADS-R have significant false-positive rates. For example, one study found the AQ had a specificity of 0.29, incorrectly flagging nearly three-quarters of non-autistic adults. The AQ sum score serves better as an index of autistic traits than a diagnostic or triage tool.

What should I expect from a proper adult autism evaluation?

A proper assessment is multistep and multidisciplinary, performed by trained professionals. It considers current and past behavior, early development, and functional impairment across social, occupational, and daily living domains. Clinicians may use self-report, observation-based, and informant-based tools. Bringing childhood records or family recollections can be invaluable because autism must have been present in early development.

Why might women with autism be misdiagnosed more often?

In one study, women with autism were more likely than men to report perceived misdiagnoses (31.7% vs. 16.7%) and had a higher frequency of prior psychiatric diagnoses (65.8% vs. 34.2%). This pattern highlights the need for a more diligent, nuanced diagnostic approach for women presenting with psychiatric concerns. Women may need to advocate for themselves during evaluation.

I'm an adult who was just diagnosed with autism — when should I get a second opinion on the diagnosis?

A second opinion is worth considering when the evaluation relied heavily on screening questionnaires rather than a full multidisciplinary assessment. The AQ has shown specificity as low as 0.29, and the RAADS-R produced 97% sensitivity and 100% specificity in a 2011 validation but failed to replicate in 2019–2021 studies. The ADOS-2 Module 4 missed about 35% of autistic adults. Because 70–80% of autistic adults have another psychiatric condition, and roughly 1 in 4 report a prior misdiagnosis, confirming the diagnosis matters. Diagnostic Detectives Network provides independent expert second opinions.

Source Information

This patient-friendly article is based on the following peer-reviewed research:

Original title: The differential diagnosis of autism spectrum disorder in adults

Authors: Hannah M. Carroll, Robyn P. Thom, and Christopher J. McDougle

Journal: Expert Review of Neurotherapeutics

Publication date: Published online April 13, 2025

DOI: 10.1080/14737175.2025.2490533

Affiliations: T.H. Chan School of Medicine, University of Massachusetts Chan Medical School (Worcester, MA); Department of Psychiatry, Lurie Center for Autism, Harvard Medical School, Massachusetts General Hospital (Lexington, MA).

Note: This article was reviewed based on the full text available at the time of writing. The original paper's section on the Social Communication Questionnaire was truncated in the source text. This patient-friendly summary is intended for educational purposes and does not replace professional medical advice.