We performed a 15 year follow-up of 748 patients undergoing bypass surgery, comparing 532 patients with one or two internal mammary artery grafts with or without additional saphenous vein grafts to 216 patients with saphenous vein grafts alone. During the 15 years of follow-up the 532 patients with at least one internal mammary artery bypass graft had better cumulative survival (p less than .01), less early recurrence of angina (p less than .01), fewer myocardial infarctions (p less than .02), fewer reoperations (p less than .001), and better cumulative event-free survival (p less than .01) than the 216 patients with vein grafts alone. Patients who developed angina postoperatively had a better cumulative survival (p less than .01) in the presence of an internal mammary graft than with vein grafts alone. The 38 patients with double internal mammary grafts had the best survival rates, with lowest recurrence of angina and rate of late myocardial infarction and no need for reoperation. We conclude the internal mammary graft gives better protection against the clinical manifestations of coronary artery disease than does the saphenous vein graft.