We describe seven cases of thrombosis of the portal and splenic vein after elective splenectomy. The diagnosis was initially unrecognized in all patients and was confused with biliary sepsis (three cases), postoperative pancreatitis (three cases), or pulmonary emboli (one case). Two patients in whom the diagnosis of portal vein thrombosis was not made within 3 days of disease onset died. In the five survivors, the diagnosis was based on clinical suspicion, confirmed with color flow Doppler ultrasonography or computed tomography with intravenous contrast material, and treated with thrombolytic agents, anticoagulants, and antibiotics. In two patients, splenic vein thrombus was visualized on initial postoperative imaging studies and the thrombus subsequently extended into the portal vein. Portal vein thrombosis should be considered in patients with fever and abdominal complaints after splenectomy. Urgent treatment with thrombolysis and anticoagulants may preserve bowel integrity and be lifesaving.