The introduction of factor VIII and IX concentrates in the early 1960s brought a significant change in the hemophiliac's life. In consequence hemophilia treatment has been improving rapidly since, and today most life-threatening hemorrhages are controlled by replacement therapy. Hemophilic arthropathy through recurrent joint and muscle bleedings occurs later in life and is often limited to one joint only. Major surgery in hemophiliacs involves little more risk than in non-hemophilic patients, provided of course there is close teamwork between surgeon and hematologist. The most frequent causes of death are no longer hemorrhages but blood-product-associated AIDS and hepatic failure. Fortunately these side effects have been overcome by the use of virus-inactivated concentrates which in Switzerland have been generally administered since 1986. Factor VIII and IX concentrates must contain a precisely declared quantity of factor VIII and IX activity respectively, with a high specific activity. High-purity concentrates should be preferred because of the hazardous effect of foreign proteins administered intravenously in large quantities over a long period. Activation of fibrinolysis with consequent failure of hemostasis or even worsening of hemorrhage may be a clinically relevant side-effect of DDAVP therapy. When DDAVP is used for prophylactic treatment before surgery, an interval of one hour between the intravenous administration of DDAVP and surgery ensures the latter is performed at the time of highest factor VIII and von Willebrand factor level but with already decreased t-PA and fibrinolytic activity. If DDAVP is used in case of hemorrhage or postoperatively, however, the whole fibrinolytic potential must be taken into account. In these cases subcutaneous administration is advantageous due to more protracted t-PA release and the subsequent lower fibrinolytic activity, which can more easily be neutralized by tranexamic acid. To prevent hemophilic arthropathy, correct replacement therapy in hemarthroses is essential: it should be performed as early as possible, preferably in a home therapy program; adequate levels of factor VIII or IX should be achieved and maintained over a sufficient length of time. Hemophiliacs who did not receive replacement therapy during childhood often need major surgery because of severely destructed joints. Joint replacement by total knee and hip prostheses has proved very successful if certain special conditions are fulfilled. Surgical indications should, however, be carefully considered and the possibilities and limits of replacement therapy should be well known. Blood-product-associated hepatitis will be of prognostic relevance in many hemophiliacs treated formerly with non-virus-inactivated concentrates.(ABSTRACT TRUNCATED AT 400 WORDS)