Whenever significant bleeding is noted in the early postoperative period, the presumption should always be that it is due to an error in surgical control of blood vessels in the operative field. Hematologic disorders that are not apparent during the long operation are most unlikely to surface as problems postoperatively. Blood transfusion reactions can cause diffuse loss of clot integrity; the sudden appearance of diffuse bleeding during an operation may be the only evidence of an intraoperative transfusion reaction. In the postoperative period, transfusion reactions usually present as unexplained fever, apprehension, and headache all symptoms difficult to interpret in the early postoperative period. Factor VIII deficiency (hemophilia) would almost certainly be known by history in a 65-year-old man, but if not, intraoperative bleeding would have been a problem earlier in this long operation. Severely hypothermic patients will not be able to form clots effectively, but clot dissolution does not occur. Care should be taken to prevent the development of hypothermia during long operations through the use of warmed intravenous fluid, gas humidifiers, and insulated skin barriers.