Attention deficit/hyperactivity disorder (ADHD) is frequently comorbid with a variety of psychiatric disorders. These disorders include oppositional defiant (ODD) and conduct disorders (CD), and affective, anxiety, and learning disorders. Studies which have examined the comorbidity of these disorders with ADHD are reviewed. ADHD and ADHD with CD seem to be distinct subtypes; children with ADHD/CD are at higher risk of antisocial personality as adults. Coexisting anxiety may attenuate impulsivity in ADHD. Studies examining stimulant response in children with ADHD/anxiety have recently yielded conflicting results. Anxiety and ADHD seem to be inherited independently. The prevalence of major depressive disorder (MDD) and bipolar disorder among children with ADHD is controversial, but there clearly exists a subgroup of severely emotionally labile children with ADHD who present serious management issues for the clinician. About 20% to 25% of children with ADHD meet criteria for a learning disorder (LD), but LD seems to be independent of ADHD.