OBJECTIVES: To examine in-hospital mortality after acute myocardial infarction in patients with diabetes mellitus. METHODS: All patients in an 800-bed teaching hospital who had a discharge diagnosis of myocardial infarction, verified by creatine kinase levels at admission, between 1991 and 1993 made up the study population. All 118 such patients who died during this period made up the case group. Two control subjects (n = 236), survivors of the hospitalization, matched by sex, age, and length of hospitalization, were selected randomly for each case. Information on the presence of diabetes mellitus, medical history, and data related to myocardial infarction were obtained through retrospective chart review. RESULTS: The mean age of all subjects in the study was 76 years. Thirty-three percent of the patients in the case group and 31% of the control subjects had a history of diabetes mellitus (odds ratio = 1.04; 95% CI, 0.64-1.70), indicating that diabetes mellitus was not associated with an increased risk of in-hospital death. The adjusted odds ratio was 1.10 (95% CI, 0.48-2.51) in patients with non-insulin-treated diabetes mellitus and 0.80 (95% CI, 0.34-1.86) in insulin-treated patients. Multivariate analysis, with conditional logistic regression, confirmed that known prognostic factors for myocardial infarction, rather than diabetic status, are predictive of in-hospital mortality. CONCLUSIONS: Once the effects of age are accounted for, the risk of in-hospital mortality is not greater in patients with diabetes mellitus than in patients without diabetes; however, diabetes mellitus may be an important factor for long-term survival.