Objective: The validity of a diagnosis of ADHD in children with a high intelligence quotient (IQ) remains controversial. Using a multidisciplinary approach, rigorous diagnostic criteria, and worldwide-validated psychometric instruments, we identified a group of children attending public schools in southern Brazil for co-occurrence of high IQ and ADHD. Method: Students attending public schools, in the first to fifth grades, were referred to our Research Center for behavioral and/or learning difficulties. These children completed clinical, psychiatric, psychological, and pedagogical evaluations for assessment of IQ, ADHD, learning, and other emotional or behavioral disorders. Results: Fifteen of the participants were identified to have a full-scale IQ [greater than or equal to] 120. Data show that 10 of these high-IQ children met the "DSM-IV" criteria diagnosis for ADHD combined type, 5 met criteria for current oppositional-defiant disorder, 2 had current major depression, and 2 had a learning disorder. Here we present the results as a case series. Conclusion: Our data support the hypothesis that ADHD is a valid diagnosis in children with high IQs. (Contains 1 figure and 1 table.)