Objectives: The natural history of human papillomavirus (HPV) infection has been studied extensively in young women; this study investigated HPV infection in adult women. Methods: Data from 3817 women aged 24–45 years in a global trial of the 4-valent HPV (6/11/16/18) vaccine were used to calculate prevalence of anogenital infections containing 9-valent (9v) HPV vaccine types (6/11/16/18/31/33/45/52/58) and five non-vaccine types (35/39/51/56/59). Incidence of infections and persistent infections was estimated for 989 placebo recipients naive to all 14 HPV types at baseline. Age-adjusted hazard ratios were calculated for various sociodemographic factors. Results: Prevalence of anogenital infection was highest in France at 29.2% (9vHPV types) and 21.7% (non-vaccine types) and lowest in the Philippines at 7.6% (9vHPV types) and 5.1% (non-vaccine types). Overall, HPV incidence (per 100 person-years) was 5.2 (9vHPV types) and 4.7 (non-vaccine types), and incidence of persistent infection was 2.7 (9vHPV types) and 2.1 (non-vaccine types). Factors associated with new HPV infections included younger age, younger age at first intercourse, being single, current use of tobacco, and higher number of past and recent sex partners. Conclusions: Because mid-adult women acquire new HPV infections, administration of the 9vHPV vaccine could reduce HPV-related morbidity and mortality in this population.