Patients with type I, or insulin-dependent, diabetes mellitus (IDDM) must comply with a complex behavioral regimen to control their diabetes. Compliance is often poor in teenage patients who are adversely influenced by peers. During a diabetes summer school, we randomly assigned 21 IDDM patients to one of two groups. One group participated in daily social-learning exercises designed to improve social skills and the ability to resist peer influence. The second group spent an equal amount of time learning medical facts about diabetes care. Four months after the intervention, hemoglobin A1 was significantly lower in the social skills intervention group. A variety of variables were significantly correlated with good metabolic control. These included self-reported compliance with a diabetes regimen and attitudes toward self-care. Unexpectedly, variables correlated with poor diabetes control included social problem-solving ability and satisfaction with social support.