Alcohol and drug use in adolescents with diabetes mellitus was assessed by an anonymous self-administered questionnaire with verification by urine drug screening. Approximately 50% of these adolescents report having tried alcohol and 25% report ongoing use. Almost 25% have tried drugs of abuse and 5% report ongoing use. One of 97 consecutive urine specimens was positive for marijuana. In general, the frequency of alcohol and drug use was less than expected based on other studies of different clinical groups of patients in the same age range. Patients with diabetes who reported drug use or who reported they live in an environment of substance abuse had poorer diabetes control than patients who did not.