A cross-sectional study of health and adjustment among 18 to 22-year-old patients with insulin-dependent diabetes mellitus (IDDM) is reported. Objectives were to examine coping with IDDM in this age group; to identify predictors of health status, treatment adherence, and health care use; and to provide a retrospective evaluation of the persistence of IDDM-specific adjustment from earlier through later adolescence. Multiple validated measures, interviews of independent informants, and biochemical assays were used to assess psychological, behavioral, and metabolic status. Patients and parents completed a retrospective measure of the patient's adjustment to IDDM during earlier adolescence. Findings (n = 81) indicated: (1) normal rates of general psychopathology but some evidence of poorer adjustment to IDDM relative to other age groups, (2) poor diabetic control and high incidence of microalbuminuria, (3) specific factors associated differentially with treatment compliance, health care use, diabetic control, and microalbuminuria among late adolescents, and (4) evidence that poor adjustment to IDDM in earlier adolescence persists into the transition to adulthood. The findings imply that late adolescents with IDDM are at risk of various unfavorable behavioral and health outcomes and that adjustment to the disease during earlier adolescence may be a predictor of subsequent health-related behavior and health status. A longitudinal study is needed to confirm these findings.