Congenital cystic lesions of the oral cavity are an extremely rare occurrence. Their prenatal diagnosis is essential since they can impede respiratory and swallowing functions. We describe a case that was detected prenatally and discuss its management. A 21-year-old primigravida patient who was 23 weeks pregnant was referred to our obstetrics and gynecology center after fetal ultrasonography showed a cystic lesion of the oral cavity. She had no family history of any congenital anomalies. Ultrasonography showed a male fetus with an anechoic mass measuring 21×11 mm encompassing the entire oral cavity, evoking either a mucocele or a cystic hygroma. Magnetic resonance imaging (MRI) showed a fetus with a wide-open mouth, due to a well-demarcated protruding cystic mass with no solid component, suggestive of a mucocele. A prenatal sonographically guided percutaneous needle aspiration of mucous fluid was performed at 33 gestational weeks. Although the mucocele decreased significantly in size, it nevertheless continued to expand progressively. After an uncomplicated pregnancy, the patient had spontaneous onset of labor at 39 weeks of gestation. An iterative aspiration was performed in the same manner in utero, resulting in a complete collapse of the mucocele. If needed, intubation could be considered. A 3030-g male was born by vaginal delivery, without respiratory distress. Clinical examination showed the extremely opened mouth and confirmed the presence of a large cystic mass approximately 4 cm in diameter, of sublingual origin and encompassing the entire oral cavity. The continuous protrusion of the tongue was responsible for the infant's inability to close the mouth and be breastfed. After insertion of a feeding tube, the newborn had maxillofacial surgery consisting in marsupialization of the cyst at 2 days of age. The mucocele decreased in size and the postoperative course was uneventful. No recurrence was observed at 6 months' follow-up. Congenital mucoceles of the tongue are very rare benign lesions of the oral cavity, resulting from extravasation or retention of mucus from minor salivary glands. Their prevalence is unknown and, to our knowledge, less than ten cases of prenatal diagnosis have been previously reported. Such cystic lesions can cause respiratory distress and swallowing disorders in newborns. They are usually suspected on ultrasonography. MRI highlights the nature of the lesion and its locoregional connections with muscles and blood vessels. It provides a good analysis of the soft tissues and can distinguish between the muscles of the tongue and the pathologic mass. However, the use of CT has been reported when the diagnosis was made after childbirth or in adulthood. Given the risks of interference of the lesion with respiratory and swallowing functions, intrauterine decompression of the mucocele can be an option to prevent respiratory distress at birth and the need for neonatal intubation. Mucoceles provide somewhat confusing and disturbing ultrasonographic appearances, which can be stressful for the medical team and parents. Prenatal diagnosis and early surgical intervention (marsupialization, complete excision of the cyst or the salivary gland) can prevent risks of breathing distress and breastfeeding problems. Therefore, this strategy is essential to offer fast and satisfactory management of this rare but anxiety-producing congenital situation.