[Hydatid cyst of the psoas muscle. Diagnosis using the CT scanner]

A 30-year-old Maroccan man was admitted with a swelling in the right iliac fossa and right flank. Serology gave negative results but ultrasonography and CT scan images were suggestive of a hydatid cyst of the psoas muscle. A cystectomy was followed by total recovery. Hydatid cysts are rarely detected in France and their clinical and diagnostic characteristics are discussed. Ultrasonography and particularly CT scaner imaging are effective diagnostic procedures, avoiding unnecessary needle punctures and enabling adequate therapeutic measures to be instituted.