A rare case of hydatid cyst of the lumbosacral spine, causing extensive destruction of the sacrum and a large pelvis mass, is reported; a cutaneous fistula from the pelvic cavity to the posterior lumbar region was also present. The patient was studied by computerized tomography and operated on by combined anterior and posterior approach. The sacral localization of the spinal hydatidosis and its extension into the pelvic cavity are unusual. CT and MR allow a good definition of the bone destruction and the abdominal and pelvic extensions. Radical removal of spinal hydatid cysts may be rarely accomplished, because of the extensive bone invasion, and multiple recurrences, requiring repeating operations, occur in most cases.