Objective: To describe the epidemiology of ADHD in communities using a DSM-IVTR case definition. Method: This community-based study used multiple informants to develop and apply a DSM -IVTR-based case definition of ADHD to screening and diagnostic interview data collected for children 5-13 years of age. Teachers screened 10,427 children (66.4%) in four school districts across two states (SC and OK). ADHD ratings by teachers and parent reports of diagnosis and medication treatment were used to stratify children into high and low risk for ADHD. Parents (n = 855) of high risk and gender frequency-matched low risk children completed structured diagnostic interviews. The case definition was applied to generate community prevalence estimates, weighted to reflect the complex sampling design. Results: ADHD prevalence was 8.7% in SC and 10.6% in OK. The prevalence of ADHD medication use was 10.1% (SC) and 7.4% (OK). Of those medicated, 39.5% (SC) and 28.3% (OK) met the case definition. Comparison children taking medication had higher mean symptom counts than other comparison children. Conclusions: Our ADHD estimates are at the upper end of those from previous studies. The identification of a large proportion of comparison children taking ADHD medication suggests that our estimates may be conservative; these children were not included as cases in the case definition, although some might be effectively treated.