The clinical and angiographic aspects of seven patients with left main stem coronary artery occlusion diagnosed within the first ten thousand coronary angiographies performed at our Hospital, are reported. The prevalence found (0.07%), is similar to that previously described (0.03 to 0.42%). Left main coronary artery occlusion is always an acute phenomenon with potentially very severe consequences. The existence of previously well developed collateral circulation from the right coronary artery, may avoid the occurrence of extensive acute myocardial infarction with cardiogenic shock and death, which otherwise follows the acute occlusion. Once diagnosed, coronary artery bypass surgery is the first choice treatment, although coronary angioplasty can be performed as a bridge for surgery, or as an alternative, if surgery is not available or is not recommended, int he acute setting of myocardial infarction. Three of our patients underwent successful angioplasty, one electively and two as an emergency during acute myocardial infarction with cardiogenic shock, and five had coronary surgery, one after previous angioplasty due to restenosis. There are only three long term survivors. In our small experience, the severe hemodynamic deterioration after left main occlusion is the major risk factor for mortality, which can only be avoided by early angiographic diagnosis.