BACKGROUND The role of factor V Leiden as a cause of Budd-Chiari syndrome has only recently been described.

AIMS To assess the specific features of factor V Leiden related Budd-Chiari syndrome.

PATIENTS Sixty three consecutive patients with hepatic vein or terminal inferior vena cava thrombosis.

RESULTS Factor V Leiden was found in 20 patients (31% (95% CI 20–43)). In the subgroup of patients with, compared with the subgroup without, factor V Leiden, a combination of prothrombotic states was more common (70% (95% CI 50–90) v 14% (95% CI 3–24)); inferior vena cava thrombosis was more frequent (40% (95% CI 19–61)v 7% (95% CI 0–14)); and distribution of initial alanine aminotransferase values was bimodal (almost normal or extremely increased) versus unimodal (p=0.003). Factor V Leiden accounted for four of five cases of massive ischaemic necrosis (transaminases >50-fold the upper limit of normal values) (p=0.014), and also for all three cases developing during pregnancy. Patients with and without factor V Leiden did not differ with regard to mortality, portosytemic shunting, or listing for liver transplantation. Hepatocellular carcinoma developed in two patients; both had factor V Leiden and indolent obstruction of the inferior vena cava.

CONCLUSIONS In patients with Budd-Chiari syndrome, factor V Leiden (a) is common; (b) precipitates thrombosis mostly when combined with another risk factor; (c) is associated with one of two contrasting clinical pictures: indolent thrombosis—particularly of the inferior vena cava—or massive ischaemic necrosis; and (d) is a major cofactor of Budd-Chiari syndrome developing during pregnancy.