The raised incidence of myocardial infarction and sudden death in diabetics was explained over 20 years ago by the increase in prevalence and severity of coronary atherosclerosis. Coronary angiographies of 820 consecutive patients admitted to hospital for coronary artery disease were analysed. One hundred and fifteen of these patients (14%) were diabetic. In 77.4% of diabetics and 72.6% of non-diabetics, coronary angiography showed coronary lesions which were usually distal and three vessel in diabetics. When the three coronary arteries were analysed globally, the percentage of patients with at least one mild stenosis was much higher in diabetics than in non-diabetics (50.6% vs 30.3% respectively, p < 0.001), but there was no statistical difference in the number of severe stenoses or occlusions. The increase in mild stenosis in the diabetic population could indicate an anatomical predisposition to future rupture of a plaque. This result could explain the increased frequency of myocardial infarction and sudden death in diabetes, not necessarily preceded clinically by angina pectoris.