[Retroperitoneal hydatid cyst: a common disease in a rare location].

Echinococcal disease remains a major problem within some endemic areas. We report a case of a single primary echinococcal cyst located in the retroperitoneal space. A 54-year-old woman, born in a rural area of southern Chile, was admitted with a 3-month history of right hip pain and painful swelling of the gluteal region. Hidatid disease was confirmed with serologic test, radiological examinations and histo-pathology. There were no cysts in any other location. A percutaneous drainage was performed and antihelminthics were administered for 12 weeks and is now being closely followed up, with good response to therapy. Especially in the endemic areas hydatid cyst should be considered when evaluating retroperitoneal cystic masses.