Mucosal high-risk (HR) human papillomaviruses (HPVs) that cause cervical and other anogenital cancers also are found in ϳ25% of head and neck carcinomas (HNCs), especially those arising in the oropharynx and the tonsils. While many HR HPV types are common in anogenital cancer, over 90% of HPV-positive HNCs harbor HPV type 16 (HPV-16). Using a quantitative colony-forming assay, we compared the ability of fulllength mucosal HPV genomes, i.e., the low-risk HPV-11 and HR HPV-16, -18, and -31, to persist in and alter the growth of primary human keratinocytes from the foreskin, cervix, and tonsils. The HR HPV types led to the formation of growing keratinocyte colonies in culture independent of the site of epithelial origin. However, HPV-18 induced colony growth in all keratinocytes >4-fold more effectively than HPV-16 or HPV-31 and >20-fold more efficiently than HPV-11 or controls. HPV-11-transfected or control colonies failed to expand beyond 32 to 36 population doublings postexplantation. In contrast, individual HR HPV-transfected clones exhibited no apparent slowdown of growth or "crisis," and many maintained HPV plasmid persistence beyond 60 population doublings. Keratinocyte clones harboring extrachromosomal HR HPV genomes had shorter population doubling times and formed dysplastic stratified epithelia in organotypic raft cultures, mirroring the pathological features of higher-grade intraepithelial lesions, yet did not exhibit chromosomal instability. We conclude that, in culture, the HR HPV type, rather than the site of epithelial origin of the cells, determines the efficacy of inducing continued growth of individual keratinocytes, with HPV-18 being the most aggressive mucosal HR HPV type tested.Human papillomaviruses (HPVs) are small DNA tumor viruses that infect, persist in, and cause proliferative lesions in the epithelial cells of the skin, ectoderm-derived mucosae, and their adnexa. Mucosal HPV types are associated with most if not all carcinomas of the uterine cervix, many anogenital cancers, and ϳ25% of head and neck cancers (HNCs) (reviewed in reference 55). HNCs arising in the oropharynx or tonsils are HPV positive in over 50% of the cases. Although the same oncogenic or "high-risk" (HR) HPV types are found in the cervix, in the anogenital area, and in HNC, their prevalence is strikingly different: in cervical and anogenital cancers, HPV type 16 (HPV-16) is found in ϳ50% of the tumors, followed by HPV-18 (ϳ20%), while the remaining cases harbor over 15 other HR HPV types, including HPV-31 and other well-characterized as well as additional, novel HPV types. In contrast, over 90 to 95% of HPV-positive HNCs contain HPV-16, whereas HPV-18, HPV-31, or other HR HPVs are infrequent (10,