Introduction: The vitelline veins are developmental vessels passing between the yolk sac and the sinus venosus of the heart during embryonic development. The splenic vein and SMV drain into the left vitelline vein and distal part of the right vitelline vein regresses. The presence of a persistent vitelline vein after birth is very rare and can be confused with umbilical vein varix. We present a rare case of a fetal persistent vitelline vein with thrombus in a neonate. Case report: A 24-years old nulliparous woman was referred at 28 weeks gestation because of fetal cystic abdominal mass near the umbilicus. Color Doppler showed venous-type turbulent flow inside the mass. It was initially thought to be the umbilical vein varix. A 2965 g female neonate was born by spontaneous vaginal delivery at 39+5weeks. Postnatal sonographic evaluation verified as Fusiform aneurysmal dilatation of extrahepatic persistent vitelline vein without internal thrombus. SMV meets persistent vitelline vein and fast flow of SMV makes blood whirling. After 4 days, Echogenic thrombus at persistent distal viltelline vein aneurysm found and the newborn was transferred to other hospital for early surgical thrombectomy. Discussion: Abnormalities of the umbilical-portal-hepatic venous system are rare congenital vascular anomalies. The first diagnosis to be considered in the abdominal midline vascular structure is umbilical vein varix. The aneurysmal vitelline vein can be distinguished from the umbilical vein varix in the course of the vessel. It is running downward and below the gallbladder in the sagittal plane. Though vitelline vein aneurysm is an extremely rare anomaly, it rapidly progresses to portal vein thrombosis that requires prompt diagnosis and treatment. Therefore, if an abnormal abdominal vascular structure is found during prenatal ultrasonography, persistent vitelline vein should be included in the differential diagnosis.