Venous thromboembolism occurs commonly in patients with cancer. The pathogenetic mechanisms of thrombosis involve a complex interaction between tumour cells, the haemostatic system, and characteristics of the patient. Among risk factors for thromboembolism are long-term immobilisation, especially in hospital, surgery, and chemotherapy with or without adjuvant hormone therapy. Although prophylaxis and treatment of thromboembolism in patients with cancer draw on the agents that are commonly used in those without cancer, there are many special features of patients with cancer that make use of these drugs more challenging. Low-molecular-weight heparins are the cornerstone of prophylaxis and treatment of venous thromboembolism in patients with cancer. These drugs have the potential to increase survival, at least in patients with more favourable outlook. About 10% of patients with idiopathic venous thromboembolism have an underlying malignant disorder that can be detected by extensive diagnostic investigation. However, the issue of whether screening for occult malignant disease ultimately improves prognosis and survival remains to be resolved.