Journal of the National Cancer Institute, April 5, 2011. Authors: Ana Cecilia Rodríguez, Mark Schiffman, Rolando Herrero, Allan Hildesheim, Concepción Bratti, Mark E. Sherman, Diane Solomon, Diego Guillén, Mario Alfaro, Jorge Morales, Martha Hutchinson, Hormuzd Katki, Li Cheung, Sholom Wacholder, Robert D. Burk Background The natural history of human papillomavirus (HPV) infections in older women is critical for preventive strategies, including vaccination and screening intervals, but is poorly understood. In a 7-year population-based cohort study in Guanacaste, Costa Rica, we examined whether women’s age and the duration of carcinogenic HPV infections influenced subsequent persistence of infection and risk of cervical intraepithelial neoplasia grade 2 (CIN 2) or worse disease. Methods At enrollment, of the 9466 participants eligible for pelvic examination, 9175 were screened for cervical neoplasia using multiple methods; those with CIN 2 or worse disease were censored and treated. Participants at low risk of CIN 2 or worse (n = 6029) were rescreened at 5–7 years (passively followed), whereas higher-risk participants (n = 2115) and subsets of low-risk women (n = 540) and initially sexually inactive women (n = 410) were rescreened annually or semiannually (actively followed) for up to 7 years. HPV testing was done using a polymerase chain reaction–based method. We determined, by four age groups (18–25, 26–33, 34–41, and ≥42 years), the proportion of prevalent infections (found at baseline) and newly detected infections (first found during follow-up) that persisted at successive 1-year time points and calculated absolute risks of CIN 2 and CIN grade 3 (CIN [...]