We retrospectively evaluated the operative results in 384 patients with diabetes mellitus operated on for ischemic coronary artery disease over a six-year period compared with a random group of 396 patients selected from 2,069 nondiabetic patients who underwent operation during the same study period. In our analysis of 13 preoperative and 5 intraoperative variables, diabetics revealed a significantly increased incidence of hypertension (p less than 0.05) and a smaller proportion of men (p less than 0.05). All other variables were not significantly different. The incidence of perioperative myocardial infarction, renal failure, neurological sequelae, leg infections, or thromboembolic events was similar in diabetic and nondiabetic patients. Hospital stay, however, was significantly increased in the diabetic group (p less than 0.05). The diabetic patients requiring intraaortic balloon counterpulsation had a significantly higher incidence of all postoperative complications analyzed compared with diabetics without balloon support (p less than 0.01), whereas the nondiabetic subset requiring intraaortic balloon counterpulsation exhibited only a significantly higher incidence of renal failure (p less than 0.01) and neurological complications (p less than 0.05). These results indicate that diabetes per se does not significantly increase morbidity in coronary bypass surgery.