Attention-deficit hyperactivity disorder, as described in the American Psychiatric Association's diagnostic manual DSM III-R (1), is a broadly defined syndrome of cognitive and behavioral problems that were originally found in children, but that have been increasingly identified in adults who had similar complaints in childhood (2). This paper briefly reviews the definition and treatment of this syndrome in children, evidence for specific neurochemical abnormalities, and effects of stimulants on neurochemistry. Finally, problems of diagnosis and treatment in adults are discussed.