Primary ovarian leiomyoma is a rare benign tumor of ovary seen in women between 20- 65 years. Among all benign primary ovarian smooth muscle tumor , ovarian leiomyoma is uncommon accounting for .5- 1% of all tumors , most of these are unilateral small in size  but they may reach big size up to 11 kg  .It usually occurs in premenopausal women most of these tumors are discovered incidentally .

Patients are usually asymptomatic, and the tumor is most commonly diagnosed unintentionally by histopathological examination of ovarian tissue after an ovariectomy for solid ovarian mass.

Ovarian leiomyoma probably arises from smooth muscle cell in the ovarian hilar blood vessels , but other possible origin are cells in ovarian ligaments , smooth muscle cells or multipotential cells in ovarian stroma, undifferentiated germ cells and cortical smooth muscle metaplasia. Ovarian leiomyoma concurrently seen with uterine leiomyoma (78%), that suggest an identical hormonal stimulation.

In some instant MRI can help to determine the preoperative diagnosis, but it may be impossible to delamitate the precise origin of large tumor (uterus sub serous versus ovary) on MRI. The tumor appeared as well circumscribed low signal intensity mass on T1 weighted imaging, with mixed signal intensity on T2 weighted imaging. Area of high intensity signal on T2 weighted images corresponded to degeneration of leiomyoma.

This paper presents a case report of primary ovarian leiomyoma in 29 years old women with complaint of abdominal pain. The right ovarian mass was histologically diagnosed as ovarian leiomyoma. Unlike other smooth muscle tumors of uterine origin, there are no definite histological criteria to categories smooth muscle tumor of ovary.