Congenital ranula is a mucous retention cyst which originates from the base of the oral cavity and is caused by sublingual or submandibular canal atresia or canalization defect. As with the other tumors in the oral cavity it may cause upper airway obstruction and hypoxia immediately after delivery. In the following stages of life, apart from the respiratory problems it may cause speach, chewing and swallowing disorders. The prenatal diagnosis of congenital sublingual ranula is very rare, and it presents as an avascular and anechoic cystic mass displacing the tongue upwards on fetal ultrasonography. Polyhydramnios can develop due to the obstruction and stomach may not be visualized. The differential diagnosis includes lymphatic malformations, epulis, epignatus, tyroglossal canal cyst and hemangioma. In this paper, we present a case of ranula which was diagnosed during prenatal ultrasonographic examination. The detailed fetal ultrasound scan performed at the 31th week of gestation revealed a non-septated anechoic cyst in the oral cavity measuring 20 x 17 x 15 mm. The cyst had well-defined regular borders with no solid component. Doppler ultrasonography did not show any vascularization within the cyst. After the delivery at the 38th week of gestation, a sublingual cystic mass with regular borders measuring 1.5 x 1.5 cm was detected in the mouth of the neonate. Entubation was not required due to the absence of respiratory distress. In order to prevent difficutlies in feeding, the cystic mass was aspirated just after the delivery. A diagnosis of sublingual ranula was made based on the localization and the mucoid consistency of the cyst.