The course of a consecutive series of 271 patients who underwent coronary artery bypass for left main coronary artery obstruction (greater than or equal to 50% luminal diameter stenosis) between January, 1971, and December, 1976, at the Mid-America Heart Institute is reported. There were four (1.5%) operative deaths. All patients have been followed until their death or for 2 to 5 years with a mean follow-up of 3.8 years. There has been an incidence of acute myocardial infarction of 2.2 per 100 patient-years of follow-up, and four patients (1.5%) have required a second coronary artery bypass procedure. There have been 19 late deaths. Death was more frequent in women and in patients who had fewer than three bypasses performed. Actuarial survival at 5 years for the entire group was 88.8%. The expected survival rate of a general population matched for age and sex at 5 years is 88.4%. It is concluded that coronary artery bypass for left main coronary artery disease favorably affects longevity.