In portal vein thrombosis, various hypercoagulable conditions and inherited or acquired thrombophilias have already been described as predisposing factors. In a 33-year-old man admitted to a hospital with upper abdominal pain, a partial portal vein and upper mesenteric vein thrombosis, respectively, and a complete splenic vein thrombosis were diagnosed. Further diagnostic procedures showed no evidence for local precipitating factors or any underlying infectious, paraneoplastic or inflammatory disease. Thrombophilia screening demonstrated elevated factor VIII levels (206%) and von Willebrand factor levels (> 440%). An acute-phase reaction was excluded. Oral anticoagulant therapy with phenprocoumon was started. Factor VIII and von Willebrand factor were reproducibly elevated to high activity levels over a period of 12 months in absence of acute or chronic inflammatory reaction. Increased levels of factor VIII and von Willebrand factor may play a pathogenetic role in the development of portal, splenic, and mesenteric thrombosis.