From January, 1990 through July 1994, 615 adult patients were undergone cardiovascular operation under the cardiopulmonary bypass. Sixteen patients were suffered perioperative cerebral infarction. The etiology of the cerebral infarction was evaluated on the pre and postoperative brain CT findings by the neurologists. In the 283 coronary artery bypass operations, 4 patients suffered watershed infarction (WS) and 4 cerebral embolism. In the 252 valve operations, one WS and one embolism. In the 80 thoracic aortic operations, 5 WS and one embolism, respectively. The risk factors of WS were the elderly, emergency, the longer operative period, and the longer cardiopulmonary bypass period. The risk factor of the embolism were male, preoperative cerebral infarction, the calcified finding of the ascending aorta by the chest CT. It is important to take preventive strategies against the watershed infarction.