Venous thomboembolism (VTE) causes only about 2% of maternal deaths in the developing world but is a leading cause of direct maternal deaths in developed countries. Pregnancy increases the risk of VTE through venous stasis, changes in blood coagulability and damage to vessels. Early diagnosis of VTE depends crucially on awareness of the condition but clinical diagnosis is unreliable in pregnancy and objective testing is essential. Compression or duplex ultrasonography is used to diagnose deep venous thrombosis and a ventilation/perfusion scan for pulmonary embolism. Low molecular weight heparins are safe and effective for treatment and for thromboprophylaxis in pregnancy. All women should undergo risk assessment in early pregnancy or preferably before pregnancy. Identifying risk factors such as obesity, or a past or family history of thromboembolism, allows at-risk women to be offered thromboprophylaxis. Guidelines on thromboprophylaxis have reduced deaths after caesarean section and are now being developed for all women.