Hemophilia B patients are usually treated for the prevention and control of bleeding episodes with a plasma derivative containing the four vitamin K-dependent clotting factors (PPSB). Prothrombin complex concentrate and the French PPSB concentrate are known to be thrombogenic when used in long-term treatment of surgical patients. The present study reports two cases of thrombotic episodes following surgery in PPSB-treated hemophilia B patients. Since 1986, there has been available a factor IX (FIX) concentrate depleted of the other vitamin K-dependent clotting factors and virally inactivated by the solvent-detergent method. This preparation has been used as replacement therapy in six patients with severe hemophilia B who were to undergo orthopedic surgery. The management of the patients before and after operation was without any thrombotic complication or undesirable side effects. The present study suggests that there is a need for an FIX preparation devoid of the other vitamin K-dependent clotting factors for long-term therapy of hemophilia B patients.