We experienced a case of cervico-mediastinal bronchogenic cyst in which a cervical cystic mass was detected by prenatal ultrasonography. On prenatal ultrasound, a unilocular, well-defined and hypoechoic mass was detected in the fetal neck. The baby was born by a normal vaginal delivery at 40 weeks of gestation, and had no respiratory distress. Radiological investigations demonstrated a cyst in the cervico-mediastinal region, which displaced the trachea to the left. At the age of 32 days, an elective resection was easily performed through a right inferior collar incision after first aspirating the contents of the cyst. Prenatal sonography showing abnormal findings is effective for identifying cysts in the perinatal period and allows for the timely resection of such cysts before respiratory distress occurs.