Objective: A case of Stage IIA primary ovarian leiomyosarcoma (LMS) with an unfavorable outcome 24 months after total abdominal hysterectomy with bilateral salpingo-oophorectomy, despite chemotherapy treatment, is described. Eighteen months from surgery the patient showed peritoneal spreading with ascites, liver and lung metastases. The present study was aimed to compare tumor growth fraction with cell density, lesion stage and clinical course. Methods: The surgical specimens were evaluated by histological, histochemical, and immunocytochemical methods. Under microscopy, mitotic index (MI) was estimated, as a ratio of mitotic figures per 1,000 tumor cells. Immunohistology was also carried out to reveal some intermediate-type filamentous proteins, as histogenetic markers, and the MIB 1 monoclonal antibody was used to assess the percent of MIB1 -positive nuclei (MIB1 labeling index). Results: The histologic findings and immunohistology of the assayed intermediate filamentous proteins substantiated a diagnosis of LMS, with associated coagulation necrosis and not rare mitotic figures. A dual tumor component was observed, representing both the pleomorphic and myxoid LMS-variants. On the basis of the quantitative findings, a MI of 10.9 and a MIBl-LI of 23.1 were cal­culated, on average. Conclusions: The proliferation indices in the described variant of ovarian LMS, denote a fast growing malignancy. They agree with the tumor stage at operation and the subsequent fatal outcome.