Recent evidence suggests that squamous cell carcinoma of the vulva may have more than one etiology, with only some tumors associated with human papillomavirus (HPV). Cells infected with HPV produce a viral protein (E6) which binds to and causes rapid degradation of p53, possibly contributing to cellular transformation. In several human malignancies, point mutations of p53 alter activity of the p53 protein contributing to cellular transformation. We tested, for the first time, the possibility that HPV-negative tumors of the vulva may have a high incidence of inactivating mutations of p53; while HPV-containing vulvar tumors rarely would have p53 mutations. Twenty-one tumors of the vulva were evaluated for the presence of HPV sequences by amplication with the polymerase chain reaction (PCR) and Southern blotting. These were evaluated for p53 mutations by single strand conformation polymorphism and sequencing of PCR products. HPV DNA sequences were found in 12 of 21 (57%) cancers of the vulva; only one of these 12 (8%) HPV-positive samples had a missense mutation of p53. In contrast, four of nine (44%) HPV-negative vulvar tumors had point mutations of p53. The p53 mutations were found in only metastatic lesion and the only recurrent tumor samples suggesting that the acquisition of p53 mutations may be associated with neoplastic progression. In conclusion, alterations in p53 activity appear to be important in the development of carcinoma of the vulva.