Angiographic data and findings at operation in 118 diabetics undergoing coronary artery bypass graft have been compared with those from 98 non-diabetic patients matched for sex and age. Atherosclerosis in the epicardial arteries in diabetics is more severe than in the general population. Saphenous vein grafting and internal mammary artery anastomoses are hampered by the fragility, irregularity, calcification and thickening as well as extensive atherosclerotic plaques in diabetic vessels. However, post-operative mortality and morbidity are no higher in diabetics and the length of hospitalisation is comparable with those of non-diabetics undergoing these procedures.