INTRODUCTIONHydatid cyst of bone constitutes only 0.5-2% of all hydatidoses. The thoracic spine is the most common site of spinal hydatidoses. Primary hydatid cyst of the sacral spinal canal is rare.PRESENTATION OF CASEA 19-year-old man had cauda equina syndrome with pelvic pain 15 days ago, the pelvic radiography shows a lytic image depend on the left sacral wing. MRI showed an intra-pelvic cystic image invading the sacrum T1 hypointense and T2W hyperintense. The Hydatid serology was positive.Surgical treatment consisted of a wide drainage of hydatid cavity dug in the left sacral wing, and by which it communicated intra pelvic, with removal of the entire cyst by gentle aspiration, abundant rinsing with hypertonic saline, release and sacred roots encompassed in a puddle of fibrosis hydatid.The evolution was good with recovery of perineal sensation and anal tone. The sacroiliac joint was considered stable and did not require synthesis or reconstruction.DISCUSSIONHydatid cysts predominantly occur in liver and lungs. Involvement of other organs is uncommon. Neither surgery nor medical therapy is generally effective for bone, especially spinal hydatidosis. The initial treatment of choice is surgical excision for neural decompression and establishing diagnosis. Albendazole is the drug of choice against this disease, when suspected, presurgical use of Albendazole in Echinococcus infestations reduces risk of recurrence and/or facilitates surgery by reducing intracystic pressure.CONCLUSIONA missed diagnosis of hydatid cyst could be devastating. Hence, hydatid cyst should be kept as a differential diagnosis, when encountered with a cystic lesion of sacrum. In addition, longterm follow-up is mandatory as recurrence is high despite use scolicidal agents.