Three hundred consecutive patients received coronary arterial bypass grafts as treatment for stenosis of the left main coronary artery. Ostial stenosis was more prevalent among women (P less than 0.001). Operative (hospital) mortality was 4 percent (12 of 300). Among 148 survivors who underwent recatheterization after a mean interval of 16.5 months, the graft patency rate was 88 percent. After a minimal follow-up period of 49 months and a mean interval of 69 months, 75 percent of the survivors were asymptomatic and 94 percent were employed or fully active. The actuarial 5 year survival rate was 88.2 percent. The presence of right coronary artery disease, abnormal preoperative ventricular function and incomplete revascularization adversely affected survival, but the differences did not reach statistical significance. Comparison of this long-term follow-up study with controlled and noncontrolled studies of nonsurgical treatment of obstructions of the left main coronary artery indicates that myocardial revascularization alleviates cardiac symptoms and increases life expectancy in patients with severe atherosclerosis of this artery.