A surgical case is described of a 40-year-old hemophilia A patient with a potent factor VIII inhibitor (40 Bethesda units) suffering from a chronic cystic haematoma in the right thigh. Surgery was performed after extensive plasmapheresis and administration of a large amount of factor VIII concentrate (42,500 U on the day of operation). During the five post-operative days, the factor VIII level was maintained above 25%, which allowed control of hemorrhage. However, two serious problems, i.e., hemolytic anemia and anamnestic response of factor VIII inhibitor titer, occurred on the 6th post-operative day. The hemolytic anemia was circumvented by administering prothrombin complex concentrate every 8 hours for 12 days until the sutures were removed. There was no bleeding although the inhibitor titer rose to 460 Bethesda units.