Twelve patients with obstruction of the extrahepatic portal venous system were seen at the Tufts-New England Medical Center between 1970 and 1979; a cause for the portal vein thrombosis was detected in 11. These included pancreatic disease (4); hematologic disorders (2); postoperative complications of laparotomy (3); transhepatic gelfoam embolization of the portal vein (1); and exchange transfusion via the umbilical vein (1). Clinical features included frequent self-limited episodes of bleeding from esophageal or gastric varices; and no characteristic or clinically helpful laboratory findings. The diagnosis was usually made in patients by identifying clots in the portal vein on selective angiography of the celiac and/or superior mesenteric arteries in which the venous phase was examined. Attempts at surgical correction were largely unsuccessful. Further thrombotic episodes occurred in three patients, and led to death in one. Two patients were given chronic anticoagulation with Coumadin and Persantin for 1 and 11/2 years, respectively without further thrombosis or gastrointestinal bleeding. However, it not yet possible to assess the risks and benefits of such therapy.