Clinical results of 64 patients who underwent surgical repair for thoracic aortic aneurysms were studied, focusing on the relationship between intraoperative blood loss and postoperative morbidity. Operative mortality was 22% in the urgent repair group and 9% in the elective repair group. Deep hypothermia, operative death, postoperative complication were the factors which significantly correlated to the amount of intraoperative blood loss. In patients who received deep hypothermia, larger blood loss and higher incidence of mortality and morbidity were observed. There was a significant relationship between the lowest core temperature during cardiopulmonary bypass and the lowest platelet count. Intraoperative blood loss revealed as a strong risk factor to directly influence postoperative clinical outcome of thoracic aortic operation.