A total of 178 patients having a diagnosis of left main coronary artery stenosis were divided into three groups as follows: surgical, Group I (n = 135 patients); operable medically treated, Group II (n = 21 patients); and inoperable, Group III (n = 22 patients). Groups 1 and 2 were comparable with regard to clinical profile, extent of anatomic coronary disease, and left ventricular function. Inoperable patients had a much higher incidence of prior myocardial infarction (especially anterior), more severe distal coronary disease, and markedly depressed left ventricular function. The hospital mortality rate for surgical patients was 4% (6/135). The late mortality rate, (median follow-up = 23.4 months) was 7% (9/135). For operable patients, the late mortality rate was 43% (9/21) at 28 months. In the inoperable group, the late death rate at 20 months was 59% (13/22). Actuarial survival at 24 months for the three groups was: 88%, 66%, and 42%, respectively. Of the nine patients who died in the operable group, two had less than 75% obstruction of the left main coronary artery and two had normal left ventricular wall motion. Although patients with higher grades of left main coronary artery stenosis and reduced left ventricular function are at greater risk, patients with less obstruction and good left ventricular function are also at risk and should have myocardial revascularization with some sense of urgency. The population of left main coronary artery stenosis is a heterogeneous one, and comparison of surgical versus medical therapy should exclude inoperable patients. The operative mortality rate has been greatly reduced in recent years (2% in the last 100 cases); this is attributed to careful monitoring in the critical prebypass period, aggressive pharmacologic treatment of increased preload, tachycardia, and hypertension, and improved aurgical technique, with emphasis on careful myocardial preservation. Adherence to these principles makes frequent use of the intra-aortic balloon either before or after revascularization unnecessary.