The paired vitelline veins selectively involute and form a part of the portal vein during embryonic development. The presence of a persistent vitelline vein segment after birth is very rare and can be confused with anomalies of the portal and umbilical veins. We present sonographic, CT and MRI findings of aneurysmal dilatation of a persistent vitelline vein with thrombus in a neonate; this case was first misdiagnosed as an umbilical vein varix by prenatal US. MRI was used to identify the persistent vitelline vein segment and the remnant umbilical vein segment.