Hydatid disease of the urinary tract is uncommon, accounting for only 2-3% of cases. There are very few reported cases in the literature of pelvic hydatid cysts causing obstructive uropathy and renal failure. We report a case of pelvic hydatid cyst in a patient presenting with urinary retention and secondary complete atrophy of one kidney. The patient was treated with surgical excision of this large retrovesical cyst, along with a simple left nephroureterectomy, with rapid improvement of symptoms. Hydatid disease should be taken into consideration in the differential diagnosis of a cystic mass in any anatomic localization, especially in patients from endemic areas.