The vascular and nervous structures and their relations with the spinal nerve roots were examined in the 2nd, 3rd and 4th posterior sacral foramina in relation to percutaneous needle insertion for neuromodulation. A foraminal branch provided by the lateral sacral artery to each foramen entered the inferior lateral quadrant of each foramen, adjacent to the nerve root medially. Facing the posterior sacral aperture and around the sacral nerves, there was no venous plexus. A venous plexus was sometimes present near the median line, and always around the proximal part of the spinal ganglion. The sacral nerve roots, especially the 3rd, had a long extradural course in the foramen, presenting a potential risk of nerve lesions during procedures involving needle insertion.