OBJECTIVE The rectogenital septum (known in clinical literature as Denonvilliers' fascia) forms an incomplete partition between the rectum and the urogenital organs in both men and women. It is composed of collagenous and elastic fibers and smooth muscle cells intermingled with nerve fibers emerging from the autonomic inferior hypogastric plexus. The aim of this study was to investigate the fetal development of the rectogenital septum, and the origin and innervation of the longitudinal smooth muscle cells within the septum, as well as to consider possible effects on function of operations that compromise the integrity of these structures. METHODS Macroscopic dissections on embalmed human pelves and plastination histology of 40 fetal and newborn pelvic specimens were performed. By means of conventional and immunohistochemical staining methods using monoclonal and polyclonal antibodies for tissue analysis and neuronal labeling, the motor and sensory innervation of the longitudinal muscle bundles within the septum was defined. RESULTS The rectogenital septum is formed by a local condensation of mesenchymal connective tissue in the early fetal period. The longitudinal muscle bundles could be traced back to the longitudinal layer of the rectal wall, and, using the septum as a guiding structure, it was possible to identify autonomic nerve fibers and ganglion cells innervating the muscle cells and crossing the midline without detectable gender differences. CONCLUSIONS Because of a coinnervation of the rectal muscle layers and the adjacent longitudinal muscle fibers of the septum, a functional correlation between the two structures during defecation is postulated. On the basis of these findings, a safer dissection of the anterior rectal wall during rectal resection is postulated, thus limiting functional disturbance and preventing neural damage.