OBJECTIVES To examine the impact of family structure on pharmacologic stimulant use among children with Attention Deficit Hyperactivity Disorder (ADHD) METHODS We examined pharmacologic stimulant use among children with ADHD using a nationally representative, population-based sample of the National Health Interview Survey from 1997 to 2003 linked with drug event files from the Medical Expenditure Panel Survey from 1998 to 2005. We conducted stepwise multivariate logistic regression to examine the likelihood of stimulant use among children ages 2-17 years of age with a clinical diagnosis of ADHD after adjustment for sociodemographic (age, sex, race, income, health insurance, geographic region and metropolitan area), health (self-reported physical and mental health status, mental disorders, health care use), and family (single vs. dual parent household structure, parental education, family size, and household income as a fraction of federal poverty line) characteristics. We also conducted stratified analyses to examine if family characteristics (e.g., maternal education) had different impacts within single and dual parent households. RESULTS Overall, an average of 37% (95% confidence interval 33%-41%) of children with ADHD received at least one stimulant during the study period, and stimulant used varied based on children's sociodemographic and health characteristics. In multivariate analyses, associations between children's household structure, parental education, and stimulant use appeared to be mediated by access to care and children's health status. However, in full multivariate models, there remained a robust association between family size and stimulant use, with children from larger families significantly more likely to be using stimulants than their counterparts. CONCLUSIONS These findings highlight the influence that non-clinical factors, such as family size, may have in mediating the use of pharmacologic therapies for children.