Venous thromboembolism (VTE), comprising deep vein thrombosis and pulmonary embolism, is the third leading cause of death due to circulatory diseases, only behind myocardial infarction and stroke. It is also an important source of morbidity in acutely ill patients. A key element in the benefit-risk assessment of drugs used for prophylaxis of VTE is balancing their antithrombotic effect versus the risk of bleeding.