Leiomyoma is the most common benign neoplasm of the reproductive organs in women. Retroperitoneal hydropic leiomyoma is rare type of myoma. Herein, we present the case of a 46-year-old (gravida 0) woman with retroperitoneal hydropic leiomyoma that was preoperatively diagnosed as an ovarian cyst. Transvaginal sonography and abdominal computed tomography revealed a mass, measuring 8.1 × 3.8 cm, with solid and cystic components in the right pelvic cavity. The patient underwent laparoendoscopic single-site surgery for the tumor excision. During the surgery, a retroperitoneal cystic tumor was resected from the right retroperitoneal cavity. Histopathologic and microscopic examinations revealed a hydropic leiomyoma with infarction. This case is impressive because of the rare location and hydropic degeneration of the leiomyoma. Furthermore, it mimicked an ovarian cyst at its initial presentation making accurate diagnosis difficult. By warning of this case, surgeons can recognize the disease entities and provide the necessary treatment.