Abstract : Leiomyosarcoma is a rare malignant tumour composed of the smooth muscle cells. It is one of the most common sarcoma subtype. It usually occurs in middle-aged or older people, usually in the fifth decade of life. The most common location of the leiomyosarcoma is the retroperitoneal space and the abdominal cavity, although it can be diagnosed in unusual locations such as the ovary. The main symptom of leiomyosarcoma is the presence of a pathological mass in the locations characteristic for the tumour. There are no characteristic predispositions in the affected patients. The diagnosis of a leiomyosarcoma requires the involvement of multiple medical disciplines. In a 53-year-old female patient a large, pathological mass was found within the pelvis during palpation. After imaging and histological examinations a laparotomy and total abdominal hysterectomy with bilateral excision of the fallopian tubes, greater web removal and anappendectomy was performed. The lesion located on the left ovary was anomental tumour measuring 21.0cm x 22.0cm x 13.0cm. The microscopic and immunohistochemical evaluation diagnosed mass as a leiomyosarcoma T2N0M0 St IIB tumour. After surgery, the patient received four cycles of chemotherapy, which included doxorubicin and dacarbazine. A follow-up CT scan showed the presence of a cystic lesion adjacent to the vaginal stump on the right side and rectum, raising the suspicion of the recurrence.