Only 7% to 50% of children with attention-deficit/hyperactivity disorder actually are treated. Of those who begin treatment, only 18% to 50% persist in the treatment for any length of time (eg, 2 to 3 years). Thus, available data on effects of long-term medication and psychosocial treatment are sparse and problematic. This article reviews available data on long-term effects of medication (stimulant and nonstimulant) and psychosocial treatment.