ABSTRACT. Objective. To understand the importance of source of care and other factors that influence differences in asthma medication use by race and Hispanic ethnicity.Methods. The Childhood Asthma Severity Study provided 12-month, retrospective, parent-reported questionnaire data on a monthly basis for children ages <12 years in a community sample of 1002 children and their families from Connecticut and Massachusetts. Medications considered included cromolyn, 2-agonist, inhaled steroids, anticholinergics, theophylline, and systemic steroids. Information was available on demographics, insurance status, symptom severity, primary care contact, and provider practice types.Results. Black and Hispanic children received fewer 2-agonists, and Hispanic children received fewer inhaled steroids than white children after adjusting for patients' race, age, gender, insurance status, symptom severity, number of primary care visits for asthma, number of urgent visits to the regular provider, family income, maternal education, and site of care. When multivariate analyses were restricted to patients in private practice, the significant association between Hispanic ethnicity and low inhaled steroid use persisted, whereas differences in 2-agonist use by race and ethnicity changed little but became nonsignificant.Conclusion. Even within private practices, patients' race and ethnicity are associated with clinician nonadherence to national guidelines. Programs to eliminate these disparities will need both to focus on site of care and to intervene at the provider and patient levels to be successful. Pediatrics 2002;109(1). URL: http://www. pediatrics.org/cgi/content/full/109/1/e1; asthma, child, practice guidelines, health insurance, Hispanic Americans.