A high autopsy incidence, 7 of 50 cases (14%), of aortic dissection as the major cause of death in patients who died following aortocoronary saphenous vein bypass is reported. The patients ranged in age from 45 to 61 years, and all had moderately severe aortic atherosclerosis. None was hypertensive, and no significant predisposing aortic medial disease was recognized. Trauma during surgical cannulation with retrograde perfusion through atherosclerotic femoral or iliac arteries was considered the initiating event leading to ileo-aortic dissection in five of the seven patients. Damage secondary to aortic cross-clamping is suggested as the pathogenetic mechanism leading to dissection in the other two patients. In six patients, the dissection was Type I of DeBakey, and in one patient, Type II. Dissection was recognized intra-operatively in five of the seven patients. In older patients, particularly those likely to have atherosclerosis of the aorta and its main branches, vigilance regarding the possibility of aortic dissection developing during the course of cardiopulmonary bypass must be constant.