Leiomyomas are benign mesenchymal tumors mostly seen in uterus. Uterin leiomyomas are one of the most common reasons of pelvic masses seen in women whereas ovarian leiomyomas are so rare that among all benign ovarian tumours it accounts only 0,5-1 %. It’s mostly seen between ages of 20-65 which premenopausal women consist %85 of them. In this case we wanted to present a 14 years old girl who was admitted to our clinic with a 6 months history of lower quadrant abdominal pain. In the ultrasonographic evaluation, there was a solid mass with uterin echogenity extending from posterior of uterus towards left adnexia with diameters of 6 cm x 5,5 cm. The origin of the tumor was unknown and could not be revealed with ultrasonography nor MRI until diagnostic laparoscopy was performed. Ovarian tumor was removed and the final pathology was compatible with leiomyoma. When we checked the literature there were only 5 cases of ovarian leiomyoma reported under age of 20 and mostly they had bilateral character. The youngest age reported was 13. Our case is the second youngest of all reported cases and it shows a unilateral character. The other important aspect of our case is that sometimes the imaging techniques can’t be adequate for detecting the origin of tumor.