It is uncertain whether adequate preinfarction diabetes control would alter the clinical outcome in diabetic patients once myocardial infarction has occurred. This study attempts an evaluation. Diabetic patients admitted successively to the cardiac intensive care unit with their first acute myocardial infarction were enrolled and followed throughout hospitalization. Every fourth consecutive patient with infarction, but not diabetic, was assigned to a control group. All patients were kept in the cardiac care unit for at least 48 h and vital signs and cardiac arrhythmias were continuously monitored. Radionuclide ventriculography was done within 24 h of admission and again upon discharge. When feasible, patients with postinfarction angina underwent coronary balloon angioplasty. During a 1-year period, 49 diabetic patients were studied, while 18 comparable nondiabetic patients served as controls. Diabetes was considered adequately controlled in 16 patients with glycosylated hemoglobin (HbA1c) of 8.8 ± 0.7%, whereas in 33 patients diabetes was uncontrolled (HbA1c 14 ± 3%), p < 0.001. No difference was found in the extent of infarct size, occurrence of heart failure, arrhythmias, and mortality when comparing the adequately with the inadequately controlled diabetics during a hospitalization period of 11 days. In diabetics, no differences were found in the short-term clinical course after acute myocardial infarction, whether the diabetes was adequately controlled or not in the preinfarction period.