Extrahepatic portal vein aneurysm associated with a tortuous portal vein. Portal vein aneurysm is rare and its etiology is controversial. A case of extrahepatic portal vein aneurysm associated with an unusually tortuous portal vein is described. Real-time ultrasonography showed anechoic masslike lesions at the porta hepatis communicating with the superior mesenteric vein and intrahepatic portal branches. This suggested the presence of two saccular portal vein aneurysms, 27 x 21 mm and 21 x 13 mm in size. Magnetic resonance imaging and portal venography confirmed the portal vein aneurysms and an unusually tortuous portal vein curving caudally between them. The liver was histologically normal and there was no evidence of portal hypertension. It is speculated that these portal vein aneurysms may have been congenital and that the associated tortuous portal vein might have been secondary to hemodynamic changes in the portal venous system. 