Hydatidosis is an endemic, widely distributed anthropozoonosis, which involves the liver, lung and other organs [Int J Urol 13 (2006) 76-9]. We reported the case of a large retroperitoneal hydatid cyst, which is a rare situation [Hepatogastroenterology 48 (2001) 1037-9; Int Urol Nephrol 32 (2000) 41-6; J Urol (Paris) 94 (1988) 445-8]. Diagnosis was suspected with blood tests and radiological examinations. A wide incision in the right iliac fossa (such in renal graft) was performed. The cyst wall was excised partially. Before, during and following the operation, the patient was given albendazole tablets (15mg/kg per day) for 3 weeks (1 week before and 2 weeks after the surgery) with blood count and liver enzyme monitorization. Especially in the endemic areas, hydatid cyst should be remembered when evaluating cystic masses in the retroperitoneum. It can be treated successfully with surgery.