In spite of the fact that most anomalies can be accurately diagnosed prenatally, one may be confronted with an extremely rare fetal abnormality that has never been described before. We report a case of a neuroectodermal cyst arising from the posterior neuropore. After 21 weeks of gestation a fetal anechoic intra- and extra-abdominal tumor was detected. The mass grew to 75 x 41 x 33 mm at 35 weeks. Initially it was believed to be a sacrococcygeal teratoma. Serial scans and Doppler ultrasound examinations were performed, which demonstrated fetal well-being. Color Doppler imaging failed to demonstrate increased tumoral perfusion. After elective Cesarean section, the tumor was excised. The postoperative course was complicated by recurrent infections of the urinary tract due to neurological damage to the bladder. There was also impaired function of the anal sphincter. The histological finding of a monolayer of neuroepithelial cells and melanocytes led to the diagnosis of a neuroectodermal cyst.