Fifty women whose clinical vulvar appearance was compatible with that of hyperplastic or mixed vulvar dystrophy were evaluated in the Vulvovaginal Referral Unit, University of Florida, from 1980 through 1986. Histologic material from biopsies performed on these patients was reviewed. The histologic picture was consistent with the clinical diagnosis in 33 cases. Fifteen patients had lichen sclerosus with various degrees of hyperkeratosis, while one had human papillomavirus-associated vulvar intraepithelial neoplasia and another had only mild chronic inflammation. Three patients in the mixed dystrophy group developed squamous carcinoma of the vulva. Women with squamous cell hyperplasia occurring in a background of lichen sclerosus (mixed dystrophy) constitute a distinct group at higher risk of developing invasive cancer and require histologic assessment.