The lateral region of the lumbar spinal canal is subject to pathologic alterations which encroach upon the neural structures located within. In order to further understanding and facilitate communication among specialists in diverse disciplines, a subdivision of the lateral region is proposed to comprise three zones: entrance zone, mid-zone and exit zone. The anatomical boundaries of these zones are defined and the pathologic conditions of each are described, and serve as the basis for techniques of surgical decompression when clinically required.