The immune response to the quadrivalent human papillomavirus (HPV) vaccine in the non-clinical trial settings is unknown. In addition, the immune response following administration of vaccine at substantially prolonged intervals is unknown. Early indications suggest that many girls will be receiving the vaccine at prolonged intervals and that this timing may affect immunogenicity. The lack of knowledge about the immunogenicity of prolonged intervals between vaccine doses precludes evidence based recommendations for patients who are substantially late for their second or third dose. Some clinicians currently restart the series while others give the doses at the incorrect interval (unpublished observation) without the ability to counsel their patients as to their expected level of immune response or protection. Examining the immune response prior to the third dose and at one and six months after the third dose will allow a better understanding of the immunogenicity of this vaccine and immune response to booster doses. Furthermore, determining factors related to non-adherence in the adolescent age group is important and timely. As an increasing number of vaccines are being recommended to the adolescent age group, elucidating factors involved with non-adherence to the recommended dosing schedule is now critical. This information can guide interventions that aim to increase adolescent adherence to the recommended schedules. Eligible girls 9 - 17 years old receiving the quadrivalent HPV vaccine from their primary care provider will be enrolled into this study on the day of, but prior to, receiving their third HPV vaccine dose or at approximately 28 days after the third HPV dose . Blood for immunogenicity testing will be obtained up to three times throughout the study: one month (Study Day 28) and six months (Study Day 180) after the third dose (Study Day 0) for all subjects and just prior to the third dose for subjects on time for their third dose (regardless of the time interval between the first and second dose). The primary analysis will be based on comparing the geometric mean titer (GMTs) and sero-response rate of subjects receiving the vaccine doses at substantially prolonged intervals to GMTs and sero-response rate of subjects receiving the second and third dose on time. In addition, on Study Day 0, patient and parent related factors known to impact health care utilization may be measured using a questionnaire given to parents/legal guardians and 14 to 17 year old subjects. Analysis based on a health care utilization model will be used to determine factors associated with non-adherence to the vaccine schedule. Initially, all subjects meeting eligibility criteria will be enrolled regardless of timing of the second and third vaccine doses. When a study arm reaches the accrual target, it will be closed to enrollment. Enrollment for the entire study will remain open until the control and three primary experimental arms have completed enrollment One or more experimental arms may be dropped from the study after monitoring of accrual rates indicates that it/they cannot be fully enrolled in a timely fashion. Monitoring will occur monthly. Assessment of accrual rates will occur semi-annually. The primary objective is to compare the GMT one month after completing the three dose vaccination series in 9 to 17 year old subjects who received the second and/or third dose at substantially prolonged intervals to subjects who receive both the second and third dose on time after adjusting for age.