Human papillomaviruses (HPVs) are associated with neoplastic and malignant lesions of the uterine cervix. Cervical neoplasia is associated with onset of sexual activity at an early age. Therefore, this study sought to define the prevalence rates of HPV infection and cytologic abnormalities in adolescents. Sexually active females 13 to 21 years of age undergoing routine cervical cytologic screening were evaluated in the adolescent clinic of an urban hospital. Cells collected by cervicovaginal lavage from 249 subjects were analyzed for HPV DNA by Southern blot hybridization with probes for HPV types 6/11, 16, and 18. The HPV DNA was detected in 95 (38.2%) of 249 patients. Teenagers between the ages of 13 and 18 years with multiple lifetime sexual partners were at higher risk for HPV infection (38/71 [54%]) compared with patients of the same age who had only a single partner (25/74 or [34%]). Twenty (8.3%) of 241 patients had abnormal Papanicolaou smears with atypia, koilocytosis, or low-grade cervical intraepithelial neoplasia. Cytologic abnormalities were detected in 16 (17%) of 94 adolescents with HPV present, but in only 4 (2.7%) of 147 of the uninfected patients. Thus, HPV emerged as a common pathogen in female adolescents, and infected patients are at increased risk for cervical epithelial abnormalities.