Prophylaxis of thrombosis during and after surgery reduces the incidence of deep vein thrombosis and lung embolism in patients at risk. The kind of therapy applied is related to the individual risk of each patient. Antithrombotic stockings together with low-dose heparin or dextran, is recommended in low-risk patients. Alternatively intermittent pneumatic compression can be applied in these patients. In patients at high risk (hip or knee surgery) a prophylaxis regimen that has been proven efficient in this patient group must be used. Unfractionated and low-molecular-weight heparin (both also in combination with DHE), dextran and oral anticoagulants have been shown to be effective, but LMW heparin seems to be the best. Prophylaxis of thrombosis is also recommended in outpatients whose lower extremities are immobilized. The initiation of therapy, choice of medicament duration of therapy is ultimately the decision of the responsible physician, who must consider it for each individual patient.