Retroperitoneal contamination may occur during the natural history of hydatid disease. Primary hydatid cyst of the retroperitoneum is extremely rare. The authors report a case of a giant retroperitoneal hydatid cyst. Clinicians and surgeons must be aware of this possibility and follow a policy of nonsystematic puncture of an abdominal cyst and avoid spillage during surgery. Symptoms are related to the size, location, or ensuing complications of a cyst. Its occurrence should be strongly suspected ahead of any abdominal cyst, especially in an endemic area, where it may act as a parasite. Total and careful surgical excision is the gold-standard therapy.