Patients with complete occlusion of the left main coronary artery are candidates for massive myocardial infarction and sudden death and are thought to have a uniformly poor prognosis. Complete occlusion of the left main coronary artery was identified in 2 male patients among 2,546 patients undergoing cardiac catheterization over a period of 14.5 years in our institution. Both patients had angina pectoris. Left ventricular end-diastolic pressure was markedly elevated in one, and the ejection fraction was moderately to markedly reduced in both. Significant collateral flow to the left coronary system from the right coronary artery was present in both patients. Our study supports previous reports that left main coronary artery occlusion is rarely encountered during cardiac catheterization.