Laryngeal mucous cysts are rare congenital malformations of the upper aero-digestive tract. We report one case of a ductal cyst developed in the supraglottic area. The diagnosis of an antenatal malformation was suspected on the basis of a hydramnios development during pregnancy. Ultrasound scan showed a cervical anechogen mass. This led to a fetal MRI which showed the cyst extension. A management of delivery had to be prepared due to the risk of air obstruction at the birth. The treatment consisted of a marsupialization of the cyst under laryngo-endoscopic surgery. Six months follow-up showed no recurrence.