Attention deficit hyperactivity disorder (ADHD) is the most common neurobehavioral disorder diagnosed in U.S. children (1). While this disorder is most often diagnosed in children when they are in elementary school, it is increasingly being identified in preschool children (2-5). This report describes the prevalence of diagnosed ADHD among children aged 4-17 years using parent-reported data collected in a large, nationally representative health survey. Differences in the prevalence of diagnosed ADHD are examined by selected demographic and socioeconomic variables: the child's sex, race and Hispanic ethnicity, health insurance coverage, and poverty status for all children aged 4-17 and among age groups 4-5, 6-11, and 12-17.