A consecutive series of 3,707 patients over a 12 year period undergoing isolated coronary artery bypass grafting (CABG) included 250 diet/oral medication-controlled and 162 insulin-dependent patients with diabetes mellitus. Analysis of 20 pre- and 18 intra-operative variables revealed a higher incidence of hypertension, left ventricular hypertrophy, and tobacco consumption for both diabetic groups. The extent of diffuse coronary disease as judged angiographically and at operation was significantly greater in both diabetic groups than in nondiabetic CABG patients. No difference was noted in the incidence of localized coronary disease between the groups. Average number of grafts was greater in both diabetic groups. The perioperative mortality was greater for both diabetic groups (5.1% for non-insulin-dependent diabetes, 4.5% for insulin-dependent diabetes) than for nondiabetic CABG patients (2.5%). The incidences of sternotomy complications and renal insufficiency were equal in the diabetic groups and both were significantly greater than in the nondiabetic group. The number of total hospital days was also greater in both diabetic groups. Actuarially determined survival and cardiac event-free curves revealed no difference between the diabetic groups but a significant difference between both diabetic groups as compared to the nondiabetic patient population, with follow-up extending to 10 years after CABG. Results indicate that diabetic patients have quantitatively and qualitatively more coronary artery disease than nondiabetic patients and have higher perioperative morbidity and mortality and a lower long-term survival rate than nondiabetic patients. However, results continue to justify selection of patients for CABG based on clinical and anatomic criteria regardless of diabetic status. Diabetes mellitus should be considered a patient-related risk factor, both short- and long-term, following CABG.