The clinical and pathologic features of 60 smooth muscle tumors of the vagina were studied to determine the pathologic characteristics which best relate to clinical behavior and to define criteria for the diagnosis of leiomyosarcoma. Cellular atypism, mitotic activity, and tumor size and contour were examined, and their relationship to recurrence was evaluated. Only 5 neoplasms recurred, and these were all ≥3 cm, with ≥5 mitotic figures per 10 high-power fields (HPF) and various degrees of atypia. The only patient whose tumor had an infiltrating margin died with metastatic tumor in the lungs. With the exception of this 1 neoplasm, all other smooth muscle tumors of the vagina were either benign or only locally aggressive. Local excision is the treatment of choice when the tumor is well circumscribed. A neoplasm with moderate to marked atypism and ≥5 mitotic figures per 10 HPF merits the designation of leiomyosarcoma.