To elucidate the characteristics of acute myocardial infarction, preinfarct angina and postinfarct angina in diabetic patients, we compared 51 diabetics and 73 non-diabetics who had myocardial infarction and angiographically-proven coronary artery stenosis. There was no statistical difference between these 2 groups with respect to age, sex, histories of smoking, hypertension and hypercholesterolemia, and hemodynamic parameters. Mean of the number of diseased vessels and of the jeopardy scores were higher in diabetics than in non-diabetics (2.4 vs. 1.9, p < 0.01; 7.2 vs. 5.7, p < 0.02, respectively). The absence of preinfarct angina (59 vs 32%, p < 0.01) and typical chest pain of myocardial infarction was more frequent in the diabetic group than in the non-diabetic group (43 vs 15%, p < 0.005). Congestive heart failure was more common in diabetics than in non-diabetics (45 vs 14%, p < 0.005). Though there was no difference in the frequency of postinfarct angina between the 2 groups (54 vs 52%), painless myocardial ischemia during treadmill exercise tests was more frequent in diabetics than in non-diabetics (75 vs 30%, p < 0.025). Compared to diabetic patients with typical chest pain of myocardial infarction, diabetics without typical chest pain had preinfarct angina less frequently (82 vs 41%, p < 0.01), but had diabetic neuropathy (71 vs 43%, p < 0.05) and retinopathy (67 vs 32%, p < 0.025) more frequently. We concluded that diabetic patients with myocardial infarction frequently lack 1) preinfarct angina, and 2) typical chest pain of myocardial infarction. 3) They often suffer from congestive heart failure, 4) frequently accompanied by painless myocardial ischemia during exercise stress tests. Therefore, special attention should be paid for the management of diabetic patients with specific neuropathy and retinopathy.