The case of a ten-year-old girl with advanced spondylolisthesis and involvement of the cauda equina is presented. Anterior interbody fusion by the transperitoneal route gave temporary relief. Recurrent neural signs and symptoms were relieved after decompression at a second operation which included laminectomy, foraminotomy, and resection of the prominent portion of the sacrum anterior to the dura and first sacral-nerve root.