We evaluated the prognosis of 858 patients with acute myocardial infarction (MI), of whom 97 (11%) had a history of diabetes mellitus. Among patients with diabetes the 1-year mortality rate was 41% versus 26% for non-diabetic patients (p < 0.01), and the 1-year reinfarction rates were 23% and 14%, respectively (p = 0.05). Diabetic patients with a history of hypertension had a similar mortality rate as comapred with diabetic patients without hypertension. In a multivariate analysis including age and history of cardiovascular disease, diabetes did not significantly contribute to death or reinfarction. Among diabetic patients the only independent risk factor for death was age. The place and mode of death appeared similar in the two groups. Patients with and without a history of diabetes had a similar infarct size. We conclude that diabetic patients with acute myocardial infarction have a very poor prognosis. Within 1 year nearly half of them are dead and one-quarter develop reinfarction. The mode of death appeared to be similar in diabetic patients as compared with non-diabetic patients.