Clinically suspected deep vein thrombosis (DVT) or pulmonary thromboembolism (PE) should be initially treated with heparin, and an objective diagnosis obtained. In pregnancy, heparin is usually continued until delivery, following which warfarin is substituted. In the absence of pregnancy, warfarin is substituted and usually continued for 3 months after a first thrombo-embolic event. Low molecular weight heparins are increasingly preferred to unfractionated heparin in non-pregnant patients with acute DVT, because of efficacy when given by daily subcutaneous injection without routine monitoring of coagulation assays, greater efficacy, and lower risks of major bleeding and of mortality. Unfractionated heparin requires monitoring by the APTT (target ratio 1.5-2.5), and warfarin requires monitoring by the International Normalized Ratio (INR) of the prothrombin time (target ratio 2.0-3.0). Graduated elastic compression stockings reduce post-thrombotic leg symptoms after DVT. Secondary prevention is important in future high risk situations.