Around 10% of people diagnosed with ADHD also meet the criteria for autism spectrum disorder. That figure comes from population-level screening of school-aged children, though some estimates run higher depending on the study methods and age group involved. The overlap works differently in the other direction: 50 to 70% of people with autism also have ADHD, making it one of the most common co-occurring conditions in autism.
The Numbers in Context
The EPINED study, a large school-based screening effort, found that 9.8% of children with ADHD also had autism. Among children with milder, subthreshold ADHD symptoms, the rate was 5.7%. These numbers are significant because they come from a general population sample rather than a clinical one, meaning the children weren’t already seeking help for developmental concerns.
The asymmetry between the two conditions is striking. While roughly 1 in 10 people with ADHD has autism, the reverse rate is far higher. The majority of autistic individuals, between 50 and 70%, also have ADHD. This makes ADHD one of the most frequent additional diagnoses in the autism population. The reason for this lopsided pattern isn’t fully understood, but it likely reflects the fact that ADHD is far more common in the general population than autism, so even a modest overlap produces different percentages depending on which direction you measure.
Why These Conditions Co-Occur
ADHD and autism share genetic roots. Whole-genome research on families with both conditions has identified genes involved in how the brain develops and how nerve cells communicate. Several of these genes play roles in processes like how chromatin (the packaging around DNA) gets remodeled during brain development and how ion channels regulate signaling between neurons. These aren’t niche findings. The same genetic pathways show up repeatedly across large studies of both conditions, supporting the idea that ADHD and autism aren’t just coincidentally appearing together but share underlying biology.
One intriguing connection involves genes related to circadian rhythm, the body’s internal clock. Sleep problems are extremely common in both ADHD and autism, and researchers have now identified specific genes tied to circadian function that appear in families affected by both conditions. This may help explain why disrupted sleep is such a consistent feature of both diagnoses, not just a side effect but potentially part of the shared biology driving them.
Why They’re Hard to Tell Apart
ADHD and autism can look surprisingly similar in everyday life, which complicates both diagnosis and prevalence estimates. Both conditions involve difficulties with executive function, the set of mental skills that help you plan, focus, and manage your behavior. Both can cause trouble in social situations, and both often show up as difficulty holding conversations, missing nonverbal cues, or behaving in ways that seem out of step with social expectations.
The key difference often comes down to why the social difficulty exists. Children with ADHD typically understand social rules but struggle to follow them in the moment. They interrupt, blurt things out, or miss cues because their attention is elsewhere. Children with autism, on the other hand, often lack the intuitive social knowledge itself. They may not recognize what a facial expression means or understand unwritten social conventions. Parents of children with ADHD frequently describe behaviors that sound autism-like: odd speech patterns, difficulty initiating conversations, issues with personal space, and even repetitive movements. This overlap is one reason dual diagnoses were historically missed.
Until 2013, clinicians couldn’t even officially diagnose both conditions in the same person. The previous edition of the diagnostic manual explicitly prevented a dual diagnosis of ADHD and autism. When the DSM-5 was published, it removed that restriction, allowing clinicians to recognize what many families already knew: both conditions can exist in the same person at the same time. This change alone has likely increased the number of people identified with both diagnoses over the past decade.
How Having Both Affects Treatment
People who have both ADHD and autism tend to be harder to treat than those with either condition alone. Stimulant medications, the standard first-line treatment for ADHD, are less effective and less well tolerated in people who also have autism. The response rate is lower, side effects are more frequent, and there’s more variability in how well the medication works from person to person. Someone with ADHD alone might respond predictably to stimulant treatment, while someone with both conditions may need more trial and error to find the right approach.
Behavioral therapies face a similar challenge. Social skills training, which is effective for many autistic individuals, doesn’t translate as well for people who also have ADHD. Cognitive behavioral therapy shows theoretical promise for the combined presentation, but there’s limited evidence so far on how well it works or whether improvements hold over time. The overall picture is that co-occurring ADHD and autism tends to be more treatment-resistant than either condition on its own, which makes early and accurate identification especially important.
What the Overlap Means for You
If you or your child has an ADHD diagnosis and you’re noticing traits that seem autism-related, the statistics suggest this isn’t unusual. Roughly 1 in 10 people with ADHD also has autism, and many more have subthreshold traits that don’t meet full diagnostic criteria but still affect daily life. The fact that these conditions share genetic pathways and overlapping symptoms means the line between them isn’t always clean.
A formal evaluation for autism in someone with ADHD requires a clinician experienced with both conditions, precisely because the symptom overlap can make it difficult to distinguish one from the other. The behavioral differences, particularly around whether social struggles stem from impulsivity or from a genuine gap in social understanding, are often what guides the diagnostic process. Getting the diagnosis right matters because it changes what kinds of support and treatment strategies are most likely to help.