A total 30,040 pregnancies were reviewed at one institution over 5 years to determine the incidence of venous thrombotic complications. Thirty-one patients experienced such complications related to pregnancy (incidence 0.1%); 13 had deep venous thrombosis and 14 had superficial venous thrombophlebitis diagnosed by duplex ultrasound. Four had pelvic vein thrombophlebitis diagnosed by computed tomography scan; three patients (one from each group) sustained a non-fatal pulmonary embolus. Of those with deep venous thrombosis, 10 (77%) were left-sided, and three (23%) were right-sided. Three had a prior history of deep venous thrombosis and one of pulmonary embolism. Of those with superficial venous thrombophlebitis, seven (50%) were left-sided, six (43%) were right-sided, and one (7%) was bilateral. Most with deep venous thrombosis presented later in pregnancy; three in the first trimester, two in the second, three in the third, and five early postpartum. Most (10/14) with superficial venous thrombophlebitis presented within 48 hours of delivery. Distribution of thrombi in those with deep venous thrombosis was compared with 643 non-pregnant women with a similar condition. A pattern of proximal involvement on the left was found, with left common femoral vein (54% versus 28%, P = 0.03) and superficial femoral vein (62% versus 26%, P = 0.006) more often involved in pregnant patients. The average number of vein segments involved was greater on the left than the right (5.3 versus 3.7). Symptoms of chronic venous insufficiency developed in three with deep venous thrombosis (25%) and in three with superficial venous thrombophlebitis (27%). None had recurrence of deep venous thrombosis. It is concluded that venous thrombotic complications associated with pregnancy are not necessarily benign, with the risk of pulmonary embolism and chronic venous insufficiency not limited to patients with deep venous thrombosis only.