Autism and ADHD are separate diagnoses with separate defining features, and they still overlap often enough that distinguishing them takes a real assessment rather than a checklist glance. Understanding where the overlap genuinely sits, and where it does not, is what makes that assessment useful.
Different core features, one shared domain
Autism spectrum disorder is defined by differences in social communication and interaction, along with restricted or repetitive behaviours, interests, or routines, frequently alongside sensory differences. ADHD is defined by inattention, hyperactivity and impulsivity. Those are genuinely different descriptions of genuinely different things.
Where they meet is executive function: the planning, task-switching, organising and self-regulating skills that both conditions can disrupt. A review of the overlap between the two conditions in children found that deficits in executive function, social function and emotional regulation appear in both, which is exactly why the two get mistaken for each other in practice even though their formal definitions do not overlap at all. [martinez-2024-adhdasd]
The overlap is common, not rare
Estimates of how often the two co-occur in children range from roughly 30 to 50 percent, and some studies have found the comorbidity even higher in specific samples. That is a large enough overlap that a clinician assessing for one is generally expected to screen for the other, rather than treating the first diagnosis reached as the whole explanation.
- Meet criteria for both 40%
- Autism without ADHD 60%
Illustrative midpoint of the commonly cited 30-50% comorbidity range; exact figures vary by sample and assessment method.
Why both used to be impossible to diagnose together
Until 2013, the diagnostic manual in clinical use did not allow both an autism and an ADHD diagnosis in the same person, which forced clinicians to attribute every symptom to whichever condition was identified first. The DSM-5 removed that restriction, formally recognising what clinicians had observed for years: the two conditions frequently coexist, and picking one to explain everything routinely left real difficulties from the other unaddressed and untreated.
Current guidance reflects that change directly: assess for both, independently, rather than assuming the presence of one accounts for the full picture.
What actually distinguishes them in practice
The features that do not overlap are what a careful assessment leans on. Difficulty following and recalling the point of a social narrative, understanding a story or conversation’s underlying thread, has been linked more specifically to autism than to ADHD, even in situations where both conditions can visibly affect attention during the same conversation. Restricted or intensely focused interests, a strong need for routine and predictability, and sensory sensitivities point toward autism. Physical restlessness, impulsive decisions, and difficulty sustaining attention across tasks that hold no special interest point toward ADHD. Neither list is exhaustive, and a real assessment weighs the whole pattern rather than any single feature.
This article covers that broader diagnostic picture. The moment-to-moment experience of an autistic shutdown against an ADHD-related meltdown is different territory with its own mechanics, covered in our dedicated comparison of the two.
Why an accurate dual assessment matters
Having both conditions is associated with more pronounced social and executive difficulties than either alone, plus a higher likelihood of co-occurring anxiety or low mood. That combined picture is exactly why the assessment needs to be thorough rather than settling for whichever diagnosis was more visible first: treatment aimed only at ADHD will leave autism-specific difficulties, and the reverse, unaddressed.
When to seek help
Speak to a doctor for a full developmental and behavioural assessment if either set of difficulties, social and communication differences, or attention and impulsivity, is affecting daily functioning, and consider asking explicitly whether both should be assessed rather than only the more obvious one.
How MyFreud can help
Logging which specific situations are hardest, a busy social setting versus an unstructured task with no clear interest, gives an assessor real texture to work from rather than a single blended impression of “struggling”. Our ADHD guide covers the condition on its own, separate from where it overlaps with autism.