Venous thromboembolism occurs infrequently but is a leading cause of illness and death during pregnancy and the puerperium and remains a diagnostic and therapeutic challenge. In the general population the incidence of pregnancy associated VTE has been estimated to vary from 1 in 1000 to 1 in 2000 deliveries. The risk of VTE is five times higher in a pregnant woman than in a nonpregnant woman of similar age. Postpartum VTE is more common than antepartum VTE. Women with congenital abnormalities or persistent presence of antiphospholipid antibodies have an increased risk of VTE during pregnancy and the puerperium. In individuals with well defined hereditary thrombosis risk factors, such as the factor V:R506Q mutation, the factor II:G20210A variation, antithrombin-deficiency or protein C-deficiency, a relative risk of pregnancy associated VTE between 3.4 and 15.2 has been found. Women with previous VTE have an approximately 3.5 fold increased risk of recurrent VTE during pregnancy compared to non-pregnant periods. Our ability to diagnose deep-vein thrombosis clinically is generally poor and is further hampered during pregnancy since dyspnea, tachypnea, swelling and discomfort in the legs are common. Objective diagnosis is essential for treatment decisions. Exposure to radiation of less than 50,000 microGy (5 rad) has not been associated with a significant risk of fetal injury. Therefore, besides sonography, routine diagnostic procedures should be performed, if clinically necessary. Heparin does not cross the placenta and is therefore the anticoagulant treatment of choice during pregnancy. In case of acute new onset of thrombosis during pregnancy, treatment is performed like in non-pregnant patients with acute deep vein thrombosis or pulmonary embolism. There is ongoing debate, whether or not pregnant women with previous venous thrombosis should routinely receive prophylactic anticoagulation. In patients who have hereditary antithrombin deficiency, antiphospholipid antibodies, a combined abnormality or a history of a severe thrombotic event (pulmonary embolism, extended deep vein thrombosis) should be advised to use prophylactic heparin during pregnancy, starting during the first trimester. Post partum prophylaxis should be given in all women with an increased risk for VTE.