The presence of serum antiphospholipid antibodies is associated with arterial and venous thrombosis. We report two cases of portal vein thrombosis associated with serum antiphospholipid antibodies. In our two patients, systemic lupus erythematosus, chronic liver disease, hepatocellular carcinoma, myeloproliferative disorders and coagulation inhibitor deficiency were excluded after extensive tests were performed to diagnose portal vein thrombosis and after a follow-up period of 6 and 7 years, respectively. The test for serum antiphospholipid antibodies was positive on two occasions in both patients. Both patients were treated with endoscopic sclerotherapy for bleeding esophageal varices and with long term anticoagulant therapy for the prevention of recurrent thrombosis. These two cases suggest that serum antiphospholipid antibodies should be investigated in patients with portal vein thrombosis of unexplained etiology.