Ten cases of intraepithelial carcinoma, five with Bowenoid features and five with early invasion, and ten cases of invasive vulvar carcinoma were examined by in situ hybridization and Southern blot analysis using DNA probes for human papillomavirus (HPV) types 6, 11, 16, 18 and 31. HPV DNA was detected in 90% of the intraepithelial cases and in 10% of the invasive cases. All positive cases showed the presence of DNA of HPV type 16. The cases with intraepithelial lesions revealed a strong correlation between the presence of HPV type 16 DNA, cigarette smoking habit, other potential cofactors such as herpes simplex (HSV) DNA sequences and the use of contraceptive drugs, and clinicopathologic features of Bowen's type in situ squamous cell carcinoma. Similar associations were not observed among the cases with invasive disease. While HPV-16 is associated with differentiated Bowenoid type vulvar intraepithelial neoplasia, which appears to be the most common form of early carcinoma of the vulva, the same association was not seen with respect to advanced vulvar invasive squamous cell carcinoma.