We describe four cases of portal vein aneurysm that were studied with ultrasonography, color Doppler, computed tomography, and magnetic resonance imaging as well as three-dimensional power Doppler. Three-dimensional ultrasonography showed the portal aneurysm and its relationship to its portal branches in all patients and showed the portosystemic communication in three. In all cases, computed tomography or magnetic resonance imaging confirmed the three-dimensional ultrasonographic findings.