In 143 patients with vulvar carcinoma (76 cases) or vulvar intraepithelial neoplasia (VIN III, 67 cases), cervical cancer or cervical intraepithelial neoplasia CIN III lesions developed in 39 patients (27%) at some time during their life. In patients with classic keratinizing squamous cell carcinoma (KSC) of the vulva, cervical neoplasia developed in only one of 51 (2%), whereas the frequency was 10 of 25 (40%) in patients with vulvar carcinoma of the basaloid or warty type and 28 of 67 (42%) in patients with VIN III lesions. The original, paraffin-embedded surgical specimens were examined by polymerase chain reaction and type-specific molecular hybridization for human papillomavirus (HPV) DNA of the types 6, 11, 16, 18, and 33. DNA of the oncogenic types HPV 16 or HPV 33 was found in 4% of the KSCs, in 84% of the basaloid or warty carcinomas, in 90% of VIN III lesions, and in 89% of the cervical lesions. The same HPV type was found in both lesions in 81% of the patients with double primary tumors. The results support the concept that VIN III and a subgroup of vulvar carcinomas are HPV-related lesions, that they are frequently associated with another HPV-related genital primary tumor, and that these multiprimary tumors are secondary to an HPV infection involving the entire genital tract.