When orally anticoagulated patients need to have surgery, the goals of management are to minimize the risks of thromboembolism and of bleeding from the invasive procedure. Some invasive procedures can be performed while patients are fully or partially anticoagulated because bleeding is rare and/or easily controlled. When it is necessary to reverse oral anticoagulant therapy it should be interrupted for as short a time as possible, usually 4 or 5 days. Intravenous unfractionated heparin or therapeutic-dose subcutaneous low-molecular-weight heparin (LMWH) can be given as "bridging therapy" to reduce the risk of thromboembolism while oral anticoagulation is interrupted. However, the risks and benefits of bridging therapy are uncertain. Bridging therapy, particularly with LMWH, may not be very effective at preventing embolism in patients with atrial fibrillation or mechanical heart valves, and it may be associated with bleeding. My preference is to minimize the time that patients are off oral anticoagulant therapy, generally restarting warfarin the day of surgery; reserve bridging therapy for those at highest risk of thromboembolism; and to use "prophylactic" rather than "therapeutic" doses of heparin after major surgery. As major surgery markedly increases the risk of venous thromboembolism, postoperative bridging therapy should be considered for patients without an inferior vena caval filter that have had proximal deep vein thrombosis or pulmonary embolism during the previous month.