The aim of this study was to evaluate the role by which different factors, such as human papillomavirus (HPV) infection, age, dystrophic alterations, focal nature and size of the lesion, influence the biologic behavior of vulvar intraepithelial neoplasia (VIN). Sixty-nine cases of VIN were investigated (28 VIN 1, 9 VIN 2, 32 VIN 3). Follow-up was possible in 58 cases, with a mean of 31 months; no treatment was given to 3 patients, while 55 were treated either medically or surgically. Eighty-four percent of the patients were cured, recurrences were found in 11%, and 5% of the patients showed progression of the disease to carcinoma. The ratio between medical and surgical treatment was the same among the cured, recurred and progressed groups of patients. No differences with regard to focal nature of the lesion, presence of HPV infection or dystrophic alterations were observed between the three groups of patients. Only the mean age was higher in patients who showed progression of the lesion to carcinoma.