You received a diagnosis — but something doesn’t feel quite right. Maybe treatment isn’t working the way you expected. Maybe a second clinician used a different term. Maybe you’ve read about other people’s experiences and found yourself thinking: that sounds more like me.
If you’re wondering whether to seek an autism ADHD second opinion, you’re raising a legitimate clinical question — not a difficult one. Diagnoses for both autism and ADHD are based entirely on observed behavior and reported history. There is no single biological test for either condition, which means clinical judgment genuinely varies between evaluators. A second opinion isn’t a challenge to your first clinician’s competence — it’s a reasonable step toward diagnostic clarity.
If you’re not yet sure whether to pursue an evaluation at all, understanding the autism diagnosis process is a helpful starting point.
At a Glance
- Autism and ADHD are both diagnosed through behavioral observation — no blood test or brain scan can confirm either.
- Research suggests that 50 to 70% of people with autism also have ADHD, making the two conditions easy to confuse or miss in combination.
- A brief or single-session evaluation may not meet clinical standards for either diagnosis.
- Women and adults who were diagnosed later in life are particularly likely to have experienced prior misdiagnosis.
- The DSM-5 explicitly permits a diagnosis of both autism and ADHD at the same time — if you were told you can only have one, that guidance may be outdated.
Can an Autism or ADHD Diagnosis Be Wrong?
Yes — and understanding why helps you evaluate your own situation clearly.
According to the National Institute of Mental Health, Autism Spectrum Disorder is diagnosed by evaluating behavior and development. There is no single biological marker. The same is true for ADHD: NIMH notes that stress, sleep disorders, anxiety, depression, and other physical conditions can produce symptoms that closely resemble ADHD, which is why a thorough evaluation — not a brief questionnaire — is required.
When diagnosis depends on clinical interpretation, the quality of the evaluation matters enormously. A clinician’s training, experience, time spent with you, and access to collateral information (reports from people who know you well, school records, prior evaluations) all shape the outcome. An evaluator who is unfamiliar with how autism presents in adults, or in women, may reach a different conclusion than one who specializes in exactly that population.
This doesn’t mean diagnoses are arbitrary. It means they are only as strong as the evaluation behind them.
Key Takeaway: Because autism and ADHD are diagnosed behaviorally, not biologically, diagnostic accuracy depends on the depth and quality of the evaluation — which means second opinions are clinically appropriate, not unusual.
Why Autism and ADHD Are So Frequently Confused
The overlap between these two conditions is not a coincidence or a diagnostic failure — it reflects genuine biological and behavioral proximity.
Research published in Life journal (2022) found that 50 to 70% of people with autism also present with comorbid ADHD. A CDC/NSCH population analysis similarly identifies ASD and ADHD as among the most commonly co-occurring neurodevelopmental conditions. Comorbidity (the presence of two or more conditions at the same time) at this rate makes differential diagnosis — the process of distinguishing between two conditions with similar presentations — genuinely complex.
Here is where the two conditions converge and where they diverge:
- Inattention and executive dysfunction appear in both autism and ADHD. In ADHD, these tend to stem from difficulties with attention regulation. In autism, they may relate more to cognitive inflexibility or sensory overload.
- Social difficulties occur in both. In ADHD, social struggles often arise from impulsivity, poor timing, or inattention in conversation. In autism, they typically involve differences in social processing and communication — a meaningfully different root cause requiring different support.
- Sensory sensitivities are formally recognized in autism, but people with ADHD frequently report them too.
There is also a critical change in diagnostic criteria that many people are unaware of. Under the DSM-IV (used before 2013), clinicians were required to choose between an autism diagnosis and an ADHD diagnosis — they were treated as mutually exclusive. The DSM-5 removed that exclusion entirely. Today, receiving both diagnoses simultaneously is not only permitted — it is clinically appropriate when both sets of criteria are met. If your evaluation happened before 2013, or if a clinician told you that you cannot have both, that assessment may reflect outdated criteria.
Key Takeaway: The high co-occurrence of autism and ADHD, combined with their overlapping symptom profiles, means misattribution of one condition as the other — or missing one entirely — is a recognized clinical challenge, not a rare mistake.
Signs That Your Diagnosis Might Need a Second Look
Not every sense of uncertainty warrants re-evaluation. But several specific situations have clear clinical backing.
Treatment isn’t working as expected. If ADHD medication has had little effect, or if recommended supports haven’t helped, that’s a meaningful signal. A systematic review in JAMA Pediatrics (2023) identified undiagnosed or inaccurately diagnosed ASD and ADHD as linked to persistent negative outcomes — including when treatment for a misidentified condition fails to address the underlying one.
Your evaluation was brief. CHADD, the leading ADHD advocacy and clinical resource organization, is explicit that ADHD cannot be diagnosed accurately from brief office observations alone. A thorough evaluation requires detailed history across multiple life domains, standardized rating scales, and often input from others who know you well. If your evaluation consisted primarily of a short interview or a self-report questionnaire, you may not have received a comprehensive assessment.
You’re an adult who was diagnosed recently — or not diagnosed at all until adulthood. An estimated 2.21% of U.S. adults have autism, yet most diagnostic tools and clinical training have historically focused on children. Adults who were missed in childhood often present differently, and not all evaluators have specific experience with adult-onset recognition.
You’re a woman who received a psychiatric diagnosis before autism was considered. This is one of the most well-documented patterns in the literature. Research published in Frontiers in Psychiatry (2025) found that autism without intellectual disability is diagnosed later and with greater difficulty in women than in men — and that the diagnostic journey frequently includes prior misdiagnosis, particularly with Borderline Personality Disorder. A 2024 study in the Journal of Autism and Developmental Disorders found that autistic traits in women are frequently misinterpreted as symptoms of other psychiatric conditions before an autism diagnosis is reached. This pattern — anxiety, depression, or BPD diagnosed before autism — is a strong indicator that re-evaluation may be warranted.
You’ve received conflicting opinions from different clinicians. If more than one professional has given you different diagnoses, that isn’t a red flag about the field — it’s information. It means the clinical picture is complex enough that specialist input is appropriate.
If any of these apply to you, an adult autism assessment with a specialist experienced in differential diagnosis is a reasonable next step.
Key Takeaway: Brief evaluations, prior psychiatric misdiagnoses in women, treatment failure, and adult late-diagnosis patterns are all recognized clinical indicators that a diagnostic re-evaluation may be appropriate.
Who Can Give You a Second Opinion?
Not every clinician who performs diagnostics has the same scope of expertise. For a second opinion specifically, you want someone with experience in differential diagnosis — the process of carefully distinguishing between conditions with overlapping presentations — not just confirmatory assessment.
The NIMH recommends a multidisciplinary approach for ASD evaluation, involving psychologists, speech-language pathologists, and other specialists as appropriate. For a second opinion as an adult, look for:
- Neuropsychologists or clinical psychologists with specific experience in adult ASD and ADHD assessment
- Clinicians who conduct structured diagnostic interviews (not just self-report tools)
- Providers who request collateral information — reports from people who know you, school or medical records, prior evaluations
- Practices that explicitly offer re-evaluation or second-opinion services
It is worth noting that the National Autistic Society in the UK formally offers specialist assessments for people seeking second or third opinions on an autism diagnosis — a clear signal that second opinions are a recognized, expected part of the diagnostic landscape, not an exceptional circumstance.
A neuropsychological evaluation can be particularly useful when the question involves both cognitive functioning and neurodevelopmental conditions simultaneously, or when prior evaluations produced conflicting conclusions.
Key Takeaway: For a second opinion on autism or ADHD, seek a specialist in differential diagnosis — ideally a neuropsychologist or clinical psychologist with documented experience in adult and/or gender-diverse presentations of both conditions.
What a Second-Opinion Evaluation Actually Involves
A thorough second-opinion evaluation for autism or ADHD in an adult typically includes several components. Understanding what to expect helps you prepare — and helps you evaluate whether what’s being offered is genuinely comprehensive.
Developmental and medical history review. A competent evaluation covers your history from early childhood forward, not just your current presentation. Research confirms that clinicians who focus only on current symptoms — rather than comprehensive neurodevelopmental history — are more likely to miss or misidentify autism, particularly in women.
Standardized diagnostic tools. For autism, this may include the ADOS-2 (Autism Diagnostic Observation Schedule, Second Edition) — a structured observational assessment — and the ADI-R (Autism Diagnostic Interview-Revised) when caregiver interviews are possible. For ADHD in adults, tools such as the DIVA (Diagnostic Interview for ADHD in Adults) provide structured, DSM-5-aligned assessment. CHADD notes there is no single test for ADHD, and that a comprehensive evaluation using standardized tools is necessary to establish diagnosis and rule out other causes.
Cognitive and neuropsychological testing. Many second-opinion evaluations — especially when the picture is complex — include testing of memory, processing speed, attention, and executive function. This provides an objective profile of how your brain works and can help distinguish between conditions that look similar on surface behavior.
Collateral information. Input from a partner, parent, or close friend who has known you over time adds important perspective, especially for adults who mask their traits in clinical settings. Autistic masking — the process of consciously or unconsciously concealing autistic traits to conform to social expectations — is particularly well-documented in women and can lead to significant underestimation of autistic traits in a standard interview.
For a detailed, adult-specific evaluation, you can learn more about what an ADHD assessment for adults covers at Josi Health.
Key Takeaway: A comprehensive second-opinion evaluation goes well beyond a short interview — it should include developmental history, standardized tools, and often neuropsychological testing and collateral information.
Frequently Asked Questions
Can I be diagnosed with both autism and ADHD?
Yes. The DSM-5 explicitly removed the exclusion that previously prevented clinicians from diagnosing both ASD and ADHD in the same person. Before 2013, clinicians using the DSM-IV were required to choose one or the other. Today, if you meet the criteria for both, receiving both diagnoses is clinically appropriate and reflects current best practice. If you were evaluated under DSM-IV criteria and told you could not have both, a re-evaluation under current criteria may be warranted.
Is seeking a second opinion normal?
Completely. The National Autistic Society formally offers specialist assessments for individuals seeking a second or third opinion on an autism diagnosis — treating it as an expected part of the diagnostic pathway, not an unusual request. Seeking further clarity when a diagnosis affects how you understand yourself, access support, and make treatment decisions is a reasonable and well-supported step.
What if the second opinion disagrees with the first?
A disagreement between two qualified clinicians is useful information, not a dead end. It typically means the diagnostic picture is complex and warrants more thorough evaluation, not less. In this situation, a third opinion from a specialist in differential diagnosis — or a full neuropsychological evaluation — can provide a more definitive picture by combining multiple standardized tools, developmental history, and cognitive testing. Keep both reports and bring them to any future evaluations.
How should I prepare for a second-opinion evaluation?
Bring as much documentation as you can: your previous evaluation report, any prior psychiatric or psychological assessments, school records if available, and a written summary of the experiences or symptoms that led you to seek re-evaluation. If a partner, parent, or close friend can attend or complete a questionnaire about your behavior across your lifetime, that collateral perspective is highly valuable — especially for adult evaluations where early childhood information may otherwise be missing.
Does having ADHD mean I can’t also be autistic?
No — and the data suggests the opposite may be more common than not. Research estimates that 50 to 70% of people with autism also have ADHD, and CDC data confirms that nearly 78% of children with an ADHD diagnosis have at least one co-occurring condition. The two conditions share significant symptom overlap, but addressing only one when both are present means important support needs go unmet.
Next Steps
If your current diagnosis doesn’t fully account for your experience — or if you’re navigating the question of whether autism, ADHD, or both apply to you — a specialist evaluation is the clearest path forward.
At Josi Health, our adult autism assessment and ADHD assessment for adults are both designed with the complexity of adult presentations in mind. Our clinicians are experienced with differential diagnosis, late identification, gender-diverse presentations, and the nuanced overlap between these two conditions.
Getting the right answer the first time isn’t always possible. Getting it eventually — through the right evaluation — always is.
Reviewed by the Josi Health Clinical Team, Licensed Psychologists.