The lifetime prevalence of psychiatric illness was determined in 114 patients with diabetes mellitus (types I and II) who were selected randomly from patients undergoing diabetes evaluations at a large medical center. The relationship of psychiatric illness to diabetic control was studied using glycosylated hemoglobin (HbAi) and self-report measures of metabolic symptoms. Seventy-one percent of the patients had a lifetime history of at least one criteria-defmed psychiatric illness; affective and anxiety disorders were the most common diagnoses. A significant difference (p =.02) in mean glycosylated hemoglobin levels was observed comparing patients with a recent psychiatric illness (X = 10.8%) to those never psychiatrically ill (X = 9.6%). These psychiatrically ill patients also-reported more symptoms of poor metabolic control and more distress associated with these symptoms than did patients never psychiatrically ill (p <.0001 for both). The overall report of diabetes symptoms was unrelated to HbAx (p =.25) and was influenced primarily by the recent presence of psychiatric disorder (p <.0001). We conclude that emotional illness is associated with both poorer metabolic control and the increased report of clinical symptoms of diabetes.