BACKGROUND: Pylephlebitis may complicate any intra-abdominal infection and carries a high mortality rate, Acute cases are usually anticoagulated to prevent thrombus extension and enteric ischemia; however, the role of anticoagulation has not been clearly defined. METHODS: Over a 3-year period, pylephlebitis was diagnosed in 44 patients with portal vein thrombosis on computed tomography scan with fever, leukocytosis, and/or positive blood cultures, The charts were reviewed for etiology, extent of venous thrombosis, and method and results of treatment. RESULTS: Eighteen patients were hypercoagulable, due to clotting factor deficiencies (6), malignancy (8), or AIDS (4). Fifteen patients had mesenteric vein involvement, Thirty-two patients were not anticoagulated, and 5 died (3 with hypercoagutable states and 2 with normal clotting function), Twelve patients were anticoagulated, and none developed subsequent bowel infarction or died. CONCLUSION: Patients with pylephlebitis and a hypercoagulable state due to neoplasms or clotting factor deficiencies should be anticoagulated, Patients with normal clotting function and mesenteric vein involvement may also benefit, We believe anticoagulation in patients with thrombus isolated to the portal vein and normal clotting function may be unnecessary. (C) 1996 by Excerpta Medica, Inc.