Occurrence of human papillomavirus type 16 DNA in cutaneous squamous and basal cell neoplasms. Sixty-eight cutaneous squamous cell neoplasms (in situ and invasive) and 26 basal cell carcinomas from 89 patients were analyzed for DNA sequences homologous to the human papillomavirus (HPV) types found predominantly in the genital tract. Thirty-six (53%) of the squamous cell neoplasms contained HPV DNA as detected by filter or in situ hybridization analysis. The frequency of detection of HPV DNA was dependent on the site of the lesion. Of 40 genital squamous cell neoplasms (penile, vulvar, and perianal), 27 (68%) had detectable HPV DNA. In 25 of these, the HPV type was 16 or HPV-16-related, which was similar to the results for the squamous cell neoplasms of the finger (HPV DNA in 9 of 11 tumors with HPV-16 in seven). None of 16 squamous cell neoplasms from sites other than the genital tract or the finger had detectable HPV DNA. HPV DNA was detected in one of the 26 basal cell carcinomas (4%). We conclude that, for cutaneous epithelial malignancies, HPV-16 is restricted to squamous cell neoplasms of the genital tract and finger. These data are consistent with venereal transmission of HPV-16 to the periungual region and suggests a role for this virus in the evolution of squamous cell carcinoma at this site. 