What Percentage of People With ADHD Have Autism?

Roughly one in eight to one in ten children diagnosed with ADHD also meets criteria for autism spectrum disorder, putting the overlap somewhere around 10 to 13 percent depending on the study and how diagnoses were confirmed. That figure is higher than many people expect, but it actually understates how intertwined these two conditions are, because the overlap looks very different when you flip the question and ask how many autistic people have ADHD. The relationship between the two is asymmetric, shaped by decades of diagnostic rules that kept researchers from studying it, and complicated by symptoms that can look nearly identical on the surface.

Where the Numbers Come From

Two large studies give a useful bracket for the ADHD-to-autism direction. A U.S. national survey found that approximately one in eight children with a current ADHD diagnosis also carried an autism diagnosis, which works out to about 12 to 13 percent.¹ A Spanish school-based study (the EPINED study) put the number at about 10 percent of children with ADHD, with an additional 6 percent of children who had subthreshold ADHD symptoms also meeting criteria for autism.²

These numbers are almost certainly conservative. Both studies relied on existing diagnoses rather than screening every participant from scratch, and autism is famously underdiagnosed, especially in girls, in people without intellectual disability, and in those whose autistic traits are overshadowed by their ADHD symptoms. The true percentage of people with ADHD who would meet autism criteria if thoroughly evaluated is probably higher than what shows up in medical records, though exactly how much higher is hard to pin down.

The Reverse Question Looks Very Different

When you start from autism and ask how many of those individuals also have ADHD, the numbers jump dramatically. Reviews of the scientific literature place the overlap at 50 to 70 percent of autistic individuals also presenting with ADHD.³ A meta-analysis that pooled data from multiple studies found the current prevalence of ADHD among autistic people to be about 39 percent, with the lifetime prevalence slightly higher at around 40 percent.⁴

The asymmetry makes sense when you think about base rates. ADHD is far more common than autism in the general population. Because the ADHD pool is so much larger, even a modest percentage of it crossing over into autism represents a lot of people, while the same genetic and neurological links mean a much larger share of the smaller autistic population also has ADHD. This is a statistical relationship, not a claim that one condition causes the other.

Why Dual Diagnosis Was Invisible for Decades

Until 2013, the official diagnostic manual used in most clinical settings explicitly prohibited giving someone both diagnoses at the same time. The DSM-IV listed an autism diagnosis as an exclusion criterion for ADHD, meaning a clinician who identified autism first was essentially barred from also diagnosing ADHD, no matter how clearly the ADHD symptoms were present.⁵ This rule suppressed research into the overlap for years and left countless people without recognition of whichever condition was diagnosed second.

The DSM-5, published in 2013, finally allowed dual diagnosis, and the field has been playing catch-up ever since. Much of the research on co-occurrence is less than a decade old, which means the numbers are still being refined as more studies are designed to capture both conditions simultaneously. Adults who were assessed under the old rules may carry only one diagnosis when they actually meet criteria for both.

How Symptoms Blur the Line

One reason the overlap is so hard to measure is that ADHD and autism share surface-level behaviors that can point a clinician toward one diagnosis while obscuring the other. Both conditions involve difficulties with executive function, social challenges (for different underlying reasons), and emotional regulation problems. A child who struggles to maintain friendships might be doing so because of impulsive behavior and poor emotional regulation (more typical of ADHD), because of difficulty reading social cues and rigid conversational patterns (more typical of autism), or both at the same time.⁶

Executive function deficits illustrate the overlap well. Both ADHD and autism are associated with problems in planning, flexible thinking, and working memory. A meta-analysis comparing the two conditions directly found it difficult to separate their executive function profiles, partly because so many participants in studies of one condition also had traits of the other. When researchers did include a group with both diagnoses, that group tended to show the worst executive function of all, combining the flexibility and planning deficits more characteristic of autism with the response inhibition problems more characteristic of ADHD.⁷ This additive pattern suggests the two conditions stack rather than cancel each other out.

Shared Genetics, Different Brains

The high co-occurrence is not a coincidence. Family and twin studies consistently show that ADHD and autism share genetic risk factors.⁸ A large genome-wide study identified seven specific genetic loci shared between the conditions, alongside five loci that distinguished them.⁹ Both conditions are highly heritable, and the genetic architecture that raises risk for one often raises risk for the other, which is part of why they co-occur far more often than chance alone would predict.¹⁰

Despite the shared genetics, the two conditions produce somewhat different patterns in the brain. Imaging research finds that autistic individuals tend to show increased cortical thickness concentrated in the temporal regions, while ADHD is associated with more widespread thickness increases but lower overall cortical volume and surface area. People with both conditions show a unique neuroanatomical pattern that is not simply the average of the two but involves widespread cortical thickness increases alongside certain decreases in surface area.¹¹ A comparative meta-analysis found that structural brain differences were mostly distinct between the conditions, with enlarged frontal and temporal gray matter volume in autism and reduced orbitofrontal volume in ADHD, though some functional overlap exists, including shared underactivation in a brain region called the right anterior insula during tasks requiring people to stop a response.¹²

Diagnostic Delays When Both Conditions Are Present

Having both ADHD and autism tends to make each condition harder to identify, leading to longer waits for accurate diagnosis. Children with both conditions received their autism diagnosis later than children who had autism alone, and their ADHD diagnosis earlier than children who had only ADHD.¹³ The delay to both diagnoses was significantly longer in the dual-diagnosis group, and these families saw more types of specialists before getting answers.¹⁴

A separate study found that children initially diagnosed with ADHD received their autism diagnosis an average of about two years later than children identified with autism first. For girls specifically, the delay stretched to about two and a half years compared to girls without a prior ADHD diagnosis.¹⁵ The ADHD symptoms, especially hyperactivity and impulsivity, can dominate the clinical picture and make the subtler social communication differences of autism easy to miss or attribute to ADHD alone.

Gender Compounds the Problem

Women and girls face particular challenges with both conditions. ADHD in females tends to present with more inattentive symptoms and emotional dysregulation rather than the overt hyperactivity that clinicians are trained to spot. Autism in women is complicated by a similar problem: the diagnostic criteria were historically built around how the condition presents in males, and many women develop sophisticated masking strategies that hide their autistic traits in social settings.¹⁶ When a woman has both conditions, the masking of autism can combine with the internalized presentation of ADHD to produce a clinical picture that looks more like anxiety or depression than a neurodevelopmental condition. This contributes to later diagnosis and, in some cases, misdiagnosis with other psychiatric conditions entirely.

Among autistic adults, roughly a quarter report having received at least one prior psychiatric diagnosis they later came to view as a misdiagnosis, with personality disorders, anxiety disorders, and mood disorders among the most common.¹⁷ While this reflects the broader autistic population rather than only those with co-occurring ADHD, it highlights a pattern in which the true neurodevelopmental picture can be obscured for years.

What Having Both Means for Quality of Life

The practical impact of carrying both conditions is real and measurable. Autistic adults who report more ADHD symptoms also report less independence in daily activities and lower overall quality of life.¹⁸ A twin study in young adults found that high autistic traits and high ADHD traits each independently lowered quality of life across physical, psychological, social, and environmental domains, and these effects largely persisted even after accounting for anxiety and depression.¹⁹ An interesting detail from that study: the interaction between autistic and ADHD traits was not itself significant, meaning the two sets of traits each drag quality of life down on their own rather than creating some compounding multiplicative effect.

Sensory Processing Gets Worse With Both

Both ADHD and autism are associated with atypical sensory processing, but the combination amplifies the problem. Children with both conditions show more pronounced sensory differences than children with either condition alone. One study found that the dual-diagnosis group was significantly more atypical than the autism-only group across most sensory domains and showed more sensory avoidance behavior than the ADHD-only group.²⁰

What is striking is that ADHD and autism on their own can produce similar overall rates of sensory issues. One cohort study found no significant difference in the rate of atypical sensory processing between the ASD and ADHD groups, though the specific nature of their attention-related sensory problems did differ.²¹ Another study reported sensory processing problems in roughly 42 to 88 percent of children with autism and about 50 percent of children with ADHD, with the two groups differing in specific sensory subscales even when their overall level of difficulty was comparable.²² For someone living with both conditions, the sensory world can feel overwhelmingly loud, bright, and unpredictable in ways that neither diagnosis alone fully explains.

Screening Tools and Their Limitations

Identifying autism within an ADHD population is not straightforward, partly because the tools were not designed with this overlap in mind. A systematic review of autism screening and diagnostic instruments used in children with ADHD found that about two-thirds of studies reported adequate specificity for ruling out autism, but the research base was thin, especially for diagnostic (as opposed to screening) measures. The Social Communication Questionnaire was the most frequently studied tool and showed consistently good performance. However, the review flagged serious bias concerns: roughly 60 percent of the studies underrepresented girls, and 75 percent underrepresented children with intellectual disability.²³ If your screening tools were mostly validated on boys without intellectual disability, they may miss autism in exactly the people who are hardest to diagnose.

Some researchers are turning to machine learning to improve differential diagnosis. One study used algorithms trained on best-practice diagnostic instruments and achieved strong accuracy in distinguishing autism from ADHD, with a reduced set of just five features performing nearly as well as the full battery.²⁴ Clinicians working with ADHD populations are also exploring brief self-report tools like the RAADS-14 as a way to flag autistic features that might otherwise go unnoticed, with one study finding that subscores for social anxiety, mentalizing, and sensory sensitivities meaningfully separated autistic and non-autistic young adults within an ADHD clinic.²⁵

Does ADHD Medication Still Work When Autism Is Present?

This is one of the most common practical questions for people who have or suspect both conditions, and the short answer is encouraging. A study of adults with ADHD found that a co-occurring autism diagnosis did not reduce the effectiveness of standard ADHD medications in lowering ADHD symptoms, and there were no significant differences in side effects or changes to vital signs between the groups.²⁶ This does not mean every individual responds identically, and anecdotal clinical reports suggest that some autistic people are more sensitive to stimulant side effects, but the overall evidence does not support the old clinical instinct that ADHD medications are less effective or more dangerous in autistic individuals.

Prenatal Risk Factors Shared by Both Conditions

The genetic overlap between ADHD and autism extends into shared environmental risk factors during pregnancy and birth. A large nationwide cohort study found that prematurity, being small for gestational age, and congenital malformations were associated with higher risk for multiple neurodevelopmental conditions including both ADHD and autism. Maternal obesity, alcohol use during pregnancy, and smoking were also linked to elevated risk across conditions, with a clear dose-response pattern for gestational age: the earlier a baby was born, the greater the likelihood of later neurodevelopmental diagnosis.²⁷ None of these factors cause either condition on their own, but they contribute to a shared vulnerability that helps explain why the two so often co-occur.

Sleep When Both Conditions Are Present

Sleep problems are common in both ADHD and autism individually, and they appear to compound when the conditions co-occur. A study comparing autistic children, autistic children with ADHD, and neurotypical children found that the dual-diagnosis group showed the most motor activity during sleep, consistent with a pattern of restless sleep. The researchers also observed an unusual wrist temperature pattern across the groups, with neurotypical children showing the highest temperatures, followed by autistic children, and the autism-plus-ADHD group showing the lowest. Because wrist temperature is closely linked to the sleep-wake cycle and melatonin production, this pattern supports the idea that melatonin secretion is atypical in autism and potentially more disrupted when ADHD is also present.²⁸ For families dealing with both conditions, sleep difficulties are often among the most disruptive day-to-day challenges, affecting mood, behavior, and the capacity to benefit from other supports.

Racial and Demographic Disparities in Who Gets Diagnosed

The percentage of people with ADHD who are recognized as also having autism depends heavily on who is doing the evaluating and who is being evaluated. A U.S. national birth cohort study found significant racial differences in diagnostic patterns after an ADHD diagnosis was made. Asian children were considerably more likely to receive a subsequent autism diagnosis than other racial groups, while White children were more likely to receive follow-up diagnoses of anxiety disorders.²⁹ These differences almost certainly reflect a mix of genuine variation in how conditions present across populations, clinician bias in what they look for, and differences in access to specialist evaluation. The co-occurrence numbers cited in research come disproportionately from studies of White children in high-income countries, and the true prevalence in underserved populations is likely undercounted.