We studied the frequency and distribution of cellular atypia in 448 cases of vulvar dystrophy. The total frequency was 9.4%. Atypia was found almost exclusively in hyperplastic areas. Epithelial changes suggestive of human papillomavirus infection were found in 14.2% of the atypical dystrophies. During the follow-up of 78 patients with typical dystrophy, mild atypia developed in three cases, but with the continuation of medical treatment it disappeared in two cases. Eleven cases of atypical dystrophy were followed for 3-48 months; three patients with severe atypia underwent surgical treatment, and eight with mild atypia underwent medical treatment. Among the last patients, six showed regression and two, progression of the atypia.