We tested the predictive utility of the health belief model (HBM) for adherence with a complex, ongoing medical regimen in the context of a chronically ill youthful population (56 adolescent outpatients with insulin-dependent diabetes mellitus; mean age = 14 years). A three-construct model of health beliefs was tested: Threat (perceived susceptibility combined with severity), Benefits-Costs, and Cues to seek treatment. Multiple indicators of compliance were used, and metabolic control was measured by glycosylated hemoglobin. The Benefits-Costs and Cues constructs were related to compliance in the theoretically expected positive direction. Threat interacted with Benefits-Costs in the prediction of compliance and with Cues in the prediction of metabolic control. The greatest compliance was achieved with low perceived Threat and high perceived Benefits-Costs. Poor metabolic control was associated with high Threat and Cues. As age increased, adherence to the exercise, injection, and frequency components of the regimen decreased.