：Objective To investigate the histological diagnostic criteria and study the prognosis in uterine smooth muscle tumors. Methods Histologic examinations were reviewed and desmin and actin immunohistochemical staining were carried out in 79 uterine smooth muscle tumors. Results In most cases leiomyosarcoma is accompanied by active mitosis

cell atypia and coagulative necrosis

whereas leiomyomas have not shown such changes. Desmin and actin positive cytoplasm stainings were significantly lower in uterine leiomyosarcomas than that in leiomyomas. Conclusion Nuclear mitotic activity is an important but not sole criterion in the diagnosis of uterine leiomyosarcoma; the combination of cellular atypia

margin infiltration

coagulative necrosis should also be taken into consideration. Meantime

desmin or actin staining can be applied as accessary criteria in making a distinction between uterine leiomyosarcoma and leiomyoma.