INTRODUCTION: Primary ovarian leiomyoma is a rare benign tumour of the ovary seen in women between 20 and 65 years old. It is usually diagnosed incidentally during pelvic examination or pathologic examination after surgery. PRESENTATION OF CASE: We describe a case of unilateral, ovarian leiomyoma. Transvaginal ultrasonography and magnetic resonance imaging (MRI) revealed a right adnexial mass. Unilateral salpingo-oophorectomy was performed, and histological examination revealed a leiomyoma arising primarily in the ovary. The diagnosis was confirmed immunohistochemically. DISCUSSION: The tumour may be asymptomatic or may manifest with lower abdominal pain like in our case. The definitive diagnosis of these lesions is difficult prior to surgical removal. Because there is no pathognomonic symptoms or characteristic imaging findings. The correct diagnosis of an ovarian leiomyoma requires identification of the smooth muscle nature of the tumour. CONCLUSION: This rare tumour of the ovary should be considered in the differential diagnosis of solid ovarian masses. An immunohistochemical analysis is recommended for definitive diagnosis. Highlights: