A 74-year-old man was admitted with right flank pain and discomfort lasting for 2 months. CT scanning revealed a large retroperitoneal cystic mass. There were no cysts elsewhere. Serological testing revealed hydatid disease. Preoperatively he was treated by Albendazole 400 mg for 1 month and then underwent laparotomy. The entire mass was excised en bloc and intact and right hemicolectomy was simultaneously performed for excision of the adhered ascending colon. He recovered uneventfully and was discharged on the eighth day, Albendazole was given and follow-up visits were arranged for every 6 months. Total cystectomy in case of active echinococcal cysts remains the treatment of choice.