Sixty patients with diabetes mellitus who survived the coronary care unit phase of acute myocardial infarction (AMI) were followed an average of 19 months and the prognosis of diabetic patients was compared with that of 719 nondiabetic patients. The mortality rate was 25% in diabetic patients and 8% in nondiabetic patients. These patients had been entered in a Multicenter Postinfarction Program, where analysis of the total data base showed 4 significant prognostic factors: cardiac symptoms before AMI, pulmonary rales when the patient was in the coronary care unit, more than 10 ventricular premature complexes per hour recorded on Holter monitor just before discharge, and a radionuclide ejection fraction of less than 40%. Of these 4 factors, only cardiac symptoms before AMI was significantly more common in diabetic patients (57% in diabetic vs 36% in nondiabetic patients). When each of these 4 factors was stratified for severity, the mortality rate was always higher in diabetic patients. The data were examined to determine other factors in diabetic patients who died. Pulmonary rales was significantly more common in diabetic patients who died (6% in survivors vs 42% in patients who died). In a multivariate analysis of both diabetic and nondiabetic patients, 5 factors were significant determinants of prognosis. They are, in order of entry into the model, rales (p less than 0.001), ejection fraction less than 40% (p less than 0.001), diabetes (p less than 0.001), symptoms before AMI (p = 0.009), and more than 10 ventricular premature complexes per hour (p = 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)