The purpose of this phase IIB MedImmune-sponsored study was to evaluate the efficacy of the HPV-16/18 VLP vaccine in the prevention of infection with HPV-16 and/or HPV-18 in adolescent and young adult women. A vaccine that prevents, or even reduces, the incidence of the common types of high-risk HPVs, particularly HPV-16 and HPV-18, could result in significant reduction in the incidence of cervical cancer and cancer-related mortality, as well as a reduction in the incidence of surgical procedures following abnormal Pap smears.