BackgroundBecause the diagnosis of attention deficit hyperactivity disorder (ADHD) in higher education settings is rapidly becoming a contentious issue, particularly among patients with high IQs, we sought to assess the validity of diagnosing ADHD in high-IQ adults and to further characterize the clinical features associated with their ADHD.MethodWe operationalized high IQ as having a full-scale IQ⩾120. We identified 53 adults with a high IQ who did not have ADHD and 64 adults with a high IQ who met diagnostic criteria for ADHD. Groups did not differ on IQ, socio-economic status or gender.ResultsHigh-IQ adults with ADHD reported a lower quality of life, had poorer familial and occupational functioning, and had more functional impairments, including more speeding tickets, accidents and arrests. Major depressive disorder, obsessive-compulsive disorder and generalized anxiety disorder diagnoses were higher in high-IQ adults with ADHD. All other psychiatric co-morbidities, including antisocial personality disorder and substance abuse, did not differ between the two high-IQ groups. ADHD was more prevalent in first-degree relatives of adults with ADHD relative to controls.ConclusionsOur data suggest that adults with ADHD and a high IQ display patterns of functional impairments, familiality and psychiatric co-morbidities that parallel those found in the average-IQ adult ADHD population.