Between 1975 and 1985, 12 patients with complete occlusion of the main left coronary artery (MLCA) were seen. The historical, clinical, biochemical, radiological, electrocardiographic, angiographical, surgical and follow-up findings were analyzed. Eight of the 12 patients presented on admission an unstable clinical situation. A normal ECG at rest was found in only 3 patients. Exercise testing elicited definite electrocardiographic changes in 5 of 6 cases. Coronary atherosclerosis was the cause of occlusion in 11 patients; in 1 patient the underlying disease process remained unclear. Significant lesions of the right coronary artery (RCA) were found in 9 and of the left anterior descending (LAD) or circonflex (CFLX) artery in 6 patients. Global and/or regional left ventricular dysfunction at rest was present in 10 patients. Angiographically visible collateral circulation was found in all patients but its extent was variable. All patients underwent bypass surgery. There were 1 operative and 2 late deaths.