Attention-deficit/hyperactivity disorder (ADHD), previously known as attention deficit disorder, is a neurobehavioral disorder characterized by pervasive inattention and hyperactivity-impulsivity that often results in substantial functional impairment (Box). Prevalence estimates of ADHD in school-aged children have ranged from 2% to 18% in community samples (1). Although stimulant medications are an effective first-line treatment for ADHD (2), concern persists regarding the possible side effects and long-term health outcomes associated with stimulant consumption (1). Estimating the number of children who have had ADHD diagnosed and are currently taking medication for the disorder is an important step toward understanding the overall burden of ADHD in the United States. Previously, population-based estimates of medication treatment for ADHD were not available or were limited by their lack of generalizability (3--5). To estimate rates of parent-reported ADHD diagnosis and medication treatment for ADHD, CDC analyzed data from the 2003 National Survey of Children's Health (NSCH). This report describes the results of that analysis, which indicated that, in 2003, approximately 4.4 million children aged 4--17 years were reported to have a history of ADHD diagnosis; of these, 2.5 million (56%) were reported to be taking medication for the disorder. Because both substantial health risks and benefits might be associated with medication treatment for ADHD, further study of this population of children with ADHD is needed.