These practice parameters review the literature on children, adolescents, and adults with attention-deficit/hyperactivity disorder (ADHD). There are three types of ADHD: predominantly inattentive, predominantly hyperactive-impulsive, and combined. Together, they occur in as many as 10% of boys and 5% of girls of elementary school age. Prevalence declines with age, although up to 65% of hyperactive children are still symptomatic as adults. Frequency in adults is estimated to be 2% to 7%. Assessment includes clinical interviews and standardized rating scales from parents and teachers. Testing of intelligence and academic achievement usually are required. Comorbidity is common. The cornerstones of treatment are support and education of parents, appropriate school placement, and pharmacology. The primary medications are psychostimulants, but antidepressants and alpha-adrenergic agonists are used in special circumstances. Other treatments such as behavior modification, school consultation, family therapy, and group therapy address remaining symptoms.