Persons with diabetes are at higher risk for myocardial infarction and sudden death than are persons without diabetes. It has been demonstrated that the artery that occludes during acute myocardial infarction generally had less than 75% stenosis on a previous angiogram. The extent of coronary artery stenosis was analyzed for 820 consecutively examined patients who underwent coronary angiography at our institution. The patients were categorized according to the presence or absence of diabetes mellitus. The severity of stenosis was taken into consideration. Patients with diabetes had moderate (50% to 75% narrowing) stenosis much more frequently than patients without diabetes (50.6 versus 30.3%, p < 0.001). Moreover diabetes mellitus was an independent risk factor for moderate stenosis. The lesions were more frequently located on distal arteries, more frequently had a pattern of three-vessel disease, and had a trend toward more diffuse disease than described 25 years ago. This greater amount of moderate stenosis may be considered a substrate for future acute plaque rupture. It may explain the high prevalence of acute myocardial infarction and sudden death among patients with diabetes without an increase in the incidence of angina pectoris.