Management of insulin dependent diabetes mellitus (IDDM) is a complex task that requires the adolescent with IDDM recognize the interaction between diet, exercise, stress, emotions, and insulin dosage. With regularity, however, adolescents with IDDM are shown to be in less good metabolic control than younger children or young adults. The study explored the combined effects of cognitive maturity and stressful life events on metabolic control among 120 adolescents (mean age 15.2 years) with insulin dependent diabetes mellitus (IDDM). Subjects were individually administered the Hunt Paragraph Completion Method measure of cognitive maturity and the Johnson and McCutcheon inventory of stressful life events. Metabolic control was assessed by total glycosylated hemoglobin. Analysis of variance revealed significant effects on metabolic control related to sex (p < .01), cognitive maturity (p < .001), and negative life events (p < .05). Adolescents with lower cognitive maturity were more likely to have elevated glycosylated hemoglobin levels. Likewise those with more and more intensely rated negative life events had higher glycosylated hemoglobin levels. Finally, females were in less good metabolic control than their male peers. Age, positive life events and early or late onset of IDDM were not significant. (CL)