To determine whether fetal surgery in a fetus with myelomeningocele (MMC) allows normal development of rectal muscles and nerves, we analyzed the rectum after fetal surgery in a sheep model. An MMC lesion was surgically created in 13 fetal sheep at 75 days of gestation. One fetal sheep died after the lesion was created. Eight fetal sheep were repaired at 100 days of gestation; the others were not repaired, as a control (n=4). Three methods were used for fetal surgery of MMC: standard neurosurgical repair (4 fetal sheep), covering of the MMC lesion by Alloderm (2 fetal sheep), and covering of the MMC lesion by Gore-Tex (2 fetal sheep). At 140 days of gestation, fetal sheep were harvested and histo-pathological analysis was performed on the rectum using hematoxylin and eosin staining for muscles and S-100 protein staining for nerves. One fetal sheep treated by standard neurosurgical repair died before harvesting. The four untreated fetal sheep had hypoplastic longitudinal muscles of the rectum but well developed-circular muscles. In addition, the untreated fetuses had a hypoplastic submucosal nerve plexus but a well-developed intermuscular nerve plexus. In contrast, treated fetal sheep had well-developed longitudinal and circular muscles except for one sheep treated with standard neurosurgical repair. In addition, except for the same fetal sheep, treated fetal sheep had well-developed nerve plexuses. There was no difference in muscle and nerve development of the rectum among the three repair methods. Fetal surgery for repair of MMC allows normal development of rectal muscles and nerves.