Previous reports suggest that morbidity and mortality post acute myocardial infarction (AMI) are increased in patients with non-insulin-dependent diabetes (NIDDM). To obtain information in our population related to the prognosis after an AMI in diabetic patients and its major determinants, we studied 96 NIDDM patients admitted consecutively with a diagnosis of AMI. We used a control group (CG) of age and sex matched non-diabetic individuals. Patients with NIDDM had more frequently a history of angina (40 vs 23%, p < 0.001) and previous MI (30 vs 15%, p < 0.05). The AMI localization and extension, and the presence of arrhythmias were similar for both groups. Early mortality after the AMI was 22% in the NIDDM group and 12% in the CG with Odds ratio of 1.9 (CI 95% 0.91-5.15), being higher in diabetic females [2.3 (CI 95% 0.77-14.6) vs female CG and 1.5 (CI 95% 0.8-7.6) vs male NIDDM]. Extended MIs predicted higher mortality rate, especially among NIDDM patients (p < 0.05). Stepwise logistic regression test supported diabetes mellitus, per se, as a major contributor for mortality (p < 0.02), followed by MI localization and extension. The worst outcome was in NIDDM female patients of advanced age and hypertensive (p < 0.00001).