The sacral hiatus is used for access to the spinal canal in many neurosurgical and anesthesiologic procedures. The aim of the present paper is to give a review of its anatomical characteristics relevant to permit correct and uncomplicated accesses. The sacral hiatus is posteriorly closed by the superficial dorsal sacrococcygeal ligament (also called sacrococcygeal membrane) which has to be pierced in order to gain the sacral canal. The mean distance between the hiatal apex and the dural sac has been reported to be 45-60.5 mm in adults and 31.4 mm in children. The mean sacral space depth has been observed to be 4.6 mm in adults and 3.5 mm in infants. On the basis of anatomical measurements of the sacral hiatus, lower insertion angles have been suggested in infant with respect to adult subjects (21° vs. 58°).