This article is a review of what is currently known about optimal treatments for patients with attention-deficit hyperactivity disorder (ADHD). It begins with a description of assessment techniques and the differential diagnosis, which includes learning disorders, anxiety disorders, and bipolar disorder. The high rate of comorbidity in patients with ADHD and the impact of comorbidity on treatment decisions are also discussed. Detailed descriptions of various pharmacologic treatments are provided, including a description of the role of combination pharmacotherapy and the integration of nonpharmacologic therapy. A decision-making model for selecting the most appropriate pharmacologic therapy versus combining pharmacotherapy with psychosocial interventions is described. The advantages and disadvantages of various pharmacologic agents--including long-acting stimulants and atomoxetine--are examined. Particular attention is paid to the recent Multimodal Treatment Study of Attention-Deficit Hyperactivity Disorder, sponsored by the National Institute of Mental Health, which includes a comparison of long-term pharmacotherapy, behavioral therapy, or a combination thereof, as well as an evaluation of the role of community-based therapy (i.e., treatment as usual). This article focuses on children and adolescents, because most of the research on ADHD has been conducted in this age group. However, a brief section on adults is also provided.