Hydatid cysts are zoonotic parasitic infections caused by Echinococcus granulosus. Although witnessed in all body parts, the first and most important locations for this parasite are the liver and lungs. Unusually, hydatid cysts are rarely located in the pelvic region. The majority of such cysts generally develop secondary to spontaneous rupture of an hepatic hydatic cyst or due to surgical inoculation. Incidentally diagnosed in a patient admitted with the picture of acute abdomen, a case of primary hydatid cyst located in retrovesical region, an uncommon localization for hydatid cysts, is presented in this report. In patients admitted with symptoms of abdominal pain in endemic regions, and in those suspected of having unidentified cystic lesions, the unusual localization of a primary hydatid cyst should be considered.