The purpose of this study was to investigate the influence of age, coping behavior, and self-care on psychological, social, and physiologic adaptation in preadolescents and adolescents with diabetes. Children (N = 103) with insulin-dependent diabetes mellitus (IDDM) between 8 and 18 years of age and their parents participated in the study. Findings indicated that preadolescent children were significantly less depressed, less anxious, coped in more positive ways, had fewer adjustment problems, and were in better metabolic control than their adolescent counterparts. Age and secondary sexual development were related to psychosocial adaptation and metabolic control of the diabetes. Further, those who coped by avoiding their problems and who were more depressed were the most likely to have problems in both adjustment and metabolic control with 56% of the variance in metabolic control explained by the variables studied. These findings indicate that preadolescents and adolescents cope differently with a chronic illness, and that interventions should be designed to identify and help those with inappropriate coping styles.