Retroperitoneal cysts have been classified into traumatic, infective, degenerative, neoplastic, and developmental, according to their origin. This paper focuses on the developmental variety of retroperitoneal pelvic cysts, particularly those of mesothelial, mesonephric, or paramesonephric origin. Their clinical presentations depend on their location; they may be mesenteric, parovarian, or vaginal. The pathogenesis and embryologic, diagnostic, and therapeutic aspects are reviewed and a case report is presented.