The epidemiology, etiology, pathogenesis, clinical presentation, diagnostic criteria, and clinical course of attention-deficit hyperactivity disorder (ADHD) are described and the role of pharmacotherapy in the management of this disorder is discussed. ADHD is a behavioral disorder of unknown etiology characterized by inattention, impulsiveness, and hyperactivity. The behavior, which may be manifest at home, at school, or in social situations, is generally worse in settings requiring sustained attention; as a result, academic underachievement is frequently an associated problem. Although the onset usually occurs before the age of four years, ADHD is most commonly diagnosed when the child enters school. It is up to six times more common in boys than in girls. Nearly one third of all children with ADHD continue to show symptoms of the disorder in adulthood. While many questions about the pathophysiology of ADHD remain unanswered and a cure has not yet been found, pharmacotherapy can effectively control the symptoms of the disorder in most patients. Three psychostimulant medications--dextroamphetamine sulfate, methylphenidate hydrochloride, and pemoline--are considered the drugs of first choice for management of the behavioral manifestations of ADHD. Dextroamphetamine and methylphenidate are equally effective in improving the symptoms of ADHD. Pemoline, a newer agent, may be tried in patients who cannot tolerate or do not respond to these two first-line agents. Common adverse effects associated with stimulant medications include anorexia, insomnia, stomach pain, and weight loss; these are generally transient and decrease with time. Imipramine hydrochloride and desipramine hydrochloride are less effective and may produce more serious adverse effects than the psychostimulants and are therefore considered second-line agents for the treatment of ADHD. Dextroamphetamine sulfate, methylphenidate hydrochloride, and pemoline have been shown to effectively control the behavioral symptoms of ADHD. For maximum impact, pharmacotherapy should be accompanied by behavioral, educational, and psychosocial intervention.