While there have been a few references to portal vein aneurysm in the world literature, this is the first report in United States radiologic literature. During a routine evaluation for fever in one patient, an ultrasound examination suggested this unusual entity at the junction of the splenic and superior mesenteric vein. It was later confirmed by angiography. Two other patients were being investigated angiographically for gastrointestinal bleeding when portal vein aneurysms were discovered. In contrast to the central location of the first patient's aneurysm, the latter two were more distal in the portal tree. The literature is reviewed and different etiologic hypothesis discussed.