Aneurysm of the portal venous system is a rare clinical condition and may be defined as a localized fusiform or saccular dilatation of the portal system. It may be congenital or acquired. The presence of hepatic cirrhosis and portal hypertension are generally associated with acquired types. In cases with a maximum portal vein diameter of more than 20 mm, it can be mentioned as portal venous system aneurysm. Two most common anatomic localizations that these aneurysms develop are the main portal vein and the junction of splenic and superior mesenteric veins. In this report, we present a case of portal vein aneurysm, being localized at the junction of the left branch of the portal vein and umbilical vein, that was very rarely reported in the literature. Copyright © 2012 by Türkiye Klinikleri.