The authors present an unusual case of a large, pedunculated uterine leiomyoma with two-sided cystic degenerations, which mimicked a bilateral malignant ovarian tumor on ultrasonography and magnetic resonance imaging (MRI). A 32-year-old unmarried female patient presented to our outpatient clinic with complaints of abdominal distention and a palpable abdominal mass extending into the upper abdomen. Ultrasonography and MRI revealed a large solid mass with bilateral cystic areas extending into both uterine adnexa. The patient then underwent a laparotomy. Gross examination revealed normal ovaries and a pedunculated mass with two-sided prominent cystic structures originating from the uterine fundus. The tumor was excised through the peduncle and pathologic evaluation revealed a uterine leiomyoma with cystic degenerations. In conclusion, a large, pedunculated leiomyoma with two-sided cystic degenerations can mimic a bilateral malignant ovarian neoplasm on imaging studies. Therefore, uterine leiomyomas with bilateral cystic degenerations should be considered during the differential diagnosis of malignant ovarian masses.