OBJECTIVES: The aims of this systematic chart review were to determine the frequency of attention-deficit/hyperactivity disorder (ADHD) in a clinic sample of children and adolescents with autism spectrum disorders (ASD), to compare ADHD symptoms in children with Autistic Disorder, Asperger's Disorder, and pervasive developmental disorders-not otherwise specified (PDD-NOS), to compare ADHD symptoms in individuals with and without ADHD-related chief complaints, and to determine the correlation between ADHD Rating Scale (ADHD RS) scores and age. METHOD: This systematic chart review examined data from children and adolescents who were consecutively referred to a university-based autism psychopharmacology program. All individuals were diagnosed by semistructured interview for ASD and ADHD, and ADHD symptoms were assessed using ADHD RS scores. RESULTS: Of 83 children, 78% fulfilled Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV) criteria for ADHD and exceeded the 93rd percentile norm for the ADHD RS. Hyperactivity-impulsivity scores were significantly greater in individuals with autism than those with other ASDs. DSM-IV ADHD diagnosis was represented equally in individuals with and without ADHD as their chief complaints. ADHD RS hyperactivity-impulsivity and total scores were negatively correlated with age. CONCLUSION: ADHD symptoms are pervasive in clinically referred children and adolescents with ASD.