The clinical and pathologic features of 32 smooth muscle tumors of the vulva were studied to determine the pathologic characteristics that best relate to the clinical behavior and to define criteria for separating leiomyomas from leiomyosarcomas. The length of follow-up ranged from 16 months to 20 years, with a median of 9 years. None of the tumors metastasized. Of the 4 neoplasms that recurred, the 2 with infiltrating margins recurred within 1 year and of these 2, the one with more than 5 mitotic figures in 10 high-power fields (HPF) recurred 5 times within a 2-year period. Neoplasms were discovered during pregnancy in 7 patients; these were characterized by extensive myxoid change, but none of the tumors that occurred during pregnancy showed significant cellular atypism or mitotic activity. Local excision is recommended as initial therapy and also for recurrences.