OBJECTIVES: To examine selected medical services for children treated for attention-deficit/hyperactivity disorder (ADHD) in a general population setting with universal health insurance. DESIGN: Retrospective analysis of administrative prescription and health services databases spanning from 1990 to 1996. SETTING: British Columbia, Canada. PATIENTS: Children (<19 years of age) who had received the psychostimulant methylphenidate (MPH; Ritalin) on a chronic basis (chronic-MPH group), who had received MPH on any other basis (nonchronic-MPH group), and who were in a no-MPH comparison group. MAIN OUTCOME MEASURES: The number of individuals who received any of the following services based on claims submitted by qualified practitioners: 1) emergency care, 2) critical care, 3) injury-related diagnostic and treatment services, 4) complementary and alternative medical (CAM) care, and 5) other diagnostic and treatment services (audiometry and allergy testing). RESULTS: Prevalence of services users was higher among MPH-treated than nontreated children for all types of services (except critical care services in the chronic-MPH group) after adjusting for effects of age, sex, socioeconomic status, and geographic setting, with odds ratios ranging from 1.49 to 3.17. There were no differences between the 2 MPH-treated groups. CONCLUSIONS: Children treated with MPH for ADHD or presumed ADHD are more frequent users of a wide range of medical services than are other children. Findings support and extend existing evidence of increased use of medical services by this population of children. Findings have implications for service planning, including injury prevention, with these children. High utilization of audiometric, allergy, and CAM services warrants further scrutiny.