OBJECTIVE To determine prevalence rates, associated features and risk factors for psychiatric disorders subsequent to the diagnosis of IDDM in youths. RESEARCH DESIGN AND METHODS Using a longitudinal, naturalistic design, 92 youths from 8 to 13 years old at onset of IDDM were followed from their initial diagnosis. They were repeatedly assessed by semistructured interview and diagnosed by operational criteria. RESULTS By the 10th year of IDDM and the mean age of 20 years, an estimated 47.6% of the sample developed psychiatric disorder. Major depressive, conduct, and generalized anxiety disorders were the most prevalent, and major depression had a significantly higher estimated rate (27.5%) than each other disorder. The highest incidence rates were during the 1st year of the medical condition. Initial maternal psychopathology increased the risk of psychiatric disorder in the subjects, and maternal depression was a specific risk factor for depression in the subjects. Earlier psychiatric disorder in the subjects also increased the risk of later disorder. CONCLUSIONS The results converge with findings from other studies, suggesting elevated psychiatric morbidity in contemporary samples of young people with IDDM. The morbidity partly reflects the high incidence of major depression in adolescence and generalized anxiety disorder in young adulthood. Monitoring the psychological status of young patients and their mothers may help to identify diabetic children at risk for psychiatric disorder and facilitate prevention or treatment efforts. Monitoring may be particularly beneficial during the 1st year of the IDDM.