 This was a prospective observational study of healthy 9-18 year old female patients receiving either a second or third dose of HPV vaccine as part of their well child care. Immune responses to HPV types 6, 11, 16 and 18 were measured both before and 1 month after the third dose of HPV vaccine with the purpose of comparing the immune responses to HPV vaccine when administered at naturally occurring longer dosing intervals to the immune response to HPV vaccine when administered as routinely recommended. 