Of 1025 patients (912 men, 113 women) who underwent coronary artery bypass grafting and were followed up for a mean of 7.4 years, 45 (4.4%) had diabetes mellitus. Norwegian population is 1.8-2%). Early mortality was not significantly greater among diabetics than in non-diabetics (2.2 vs. 3.1%, odds ratio--OR-0.44, confidence interval--CI- 0.05-3.56). Diabetic patients had no increased risk of perioperative myocardial infarction (OR = 0.87, CI 0.36-2.10) or of low-output syndrome necessitating intraortic balloon pumping (OR = 0.42, CI 0.55-3.05), and no excess incidence of late non-fatal myocardial infarction (relative risk = 0.69, CI 0.10-1.28) or late chronic heart failure (OR = 2.50, CI 0.5-11.0). Long-term mortality was increased in the diabetic patients (relative risk 1.87, CI 1.60-2.14). Thus diabetes did not entail heightened risk of early mortality, perioperative myocardial infarction or low-output syndrome. Nor was there excess risk of recurrent angina pectoris, late non-fatal myocardial infarction or chronic heart failure among the diabetic patients, but the late mortality risk was increased.