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Of 99 consecutive patients with 101 internal mammary artery grafts, 91 of 97 hospital survivors (94%) underwent angiography 2 weeks after operation, 84 of 96 survivors (88%) after 1 year, 66 of 88 survivors (75%) after 5 years, and 37 of 69 survivors (54%) after 11 years (range 10 to 13 years). Thirty-five of the 37 patients who consented to a fourth postoperative angiographic study (95%, confidence limits 86% to 100%) still reported relieved angina 11 years after the operation, and seven patients (19%, confidence limits 5% to 33%) were completely free of symptoms. Angiographic findings in 30 patients with symptoms of angina were progression of the coronary artery disease in 22, (73%, confidence limits 56% to 91%), occluded or stenosed grafts in nine (30%, confidence limits 12% to 48%), and nonbypassed obstructions in six patients (20%, confidence limits 4% to 36%). The cumulative 11-year patency rate was 88%, confidence limits 81% to 95%, for internal mammary artery grafts and 61%, confidence limits 45% to 76% for saphenous vein grafts. Six of 18 saphenous vein grafts (33%, confidence limits 19% to 58%) occluded in the interval between 5 and 11 years after operation, and gross wall irregularities were observed in six of the 12 patent saphenous vein grafts. Unligated side branches and stenosis of the internal mammary artery did not prevent long-term graft patency. Internal mammary artery graft failures were related to technical errors during the operation and occurred when the internal mammary artery was used to bypass a low-grade coronary artery stenosis. In one patient, regression of a coronary artery stenosis was associated with a marked decrease in luminal size of the internal mammary artery graft before the 5-year follow-up. This single internal mammary artery graft became occluded in the interval between 5 and 11 years after the operation. Eleven of 36 internal mammary artery grafts (31%, confidence limits 14% to 47%) increased 15% to 40% in luminal diameter as a result of increased myocardial blood demand before the 11-year follow-up.