To evaluate receipt of≥ 1 dose of HPV vaccine by age 13 years among adolescent girls, data during 2007–2013 NIS-Teen survey years were combined and analyzed by birth cohort.†† Among girls, receipt of≥ 1 dose of HPV by age 13 years has increased an average of 5.9%(95% confidence interval [CI]= 2.8%–9.0%) with each new birth cohort, reaching 46.8%(CI= 41.2%–52.5%) for the 2000 birth cohort (Figure). Missed opportunities to receive the HPV vaccine by age 13 years also were evaluated. A missed opportunity for adolescent girls was defined as a health care encounter occurring on or after the 11th birthday and before the 13th birthday and on or after March 23, 2007 (the publication date of the ACIP HPV4 recommendation for girls), during which the adolescent received at least one vaccine but did not receive the first dose of the HPV vaccine. The percentage of unvaccinated girls at age 13 years with at least one missed opportunity for HPV vaccination ranged from 9.3%(CI= 8.1%–10.8%) for the 1994 cohort to 83.7%(CI= 77.8%–88.2%) for the 2000 cohort (Figure). If all missed opportunities for HPV vaccination had been eliminated for the 2000 birth cohort, vaccination coverage with≥ 1 dose of HPV vaccine could have reached 91.3%(CI= 87.9%–93.8%) by age 13 years, a 42.7 percentage-point difference from the actual coverage level. The percentage of parents reporting that they received a recommendation for the HPV vaccine from their clinician was significantly higher in 2013 compared with 2012 for both parents of girls (64.4% compared with 61.0%) and parents of boys (41.6% compared with 28.0%). More parents of vaccinated teens (girls: 73.7%; boys: 71.7%) reported receiving a recommendation compared with parents of unvaccinated teens (girls: 52.0%; boys: 25.7%). The 2013 NIS-Teen asked parents who reported they were not likely to vaccinate their teen in the 12 months after interviews or were unsure of their vaccination plans (girls: 23.0%[CI= 21.5%–24.6%]; boys: 37.4%[CI= 35.7%–39.1%]) to identify the main reason why their teen would remain unvaccinated. The top five responses from the parents of girls and parents of boys were the same, differing only in order of frequency (Table 2). More than 30% of the parents of girls and boys cited as their main reason lack of knowledge (girls and boys: both 15.5%) or belief that the vaccine was not needed or necessary (girls: 14.7%; boys: 17.9%). Among parents of boys, 22.8% reported that the main reason was that HPV vaccination had not been recommended; among parents of girls, 13.0% reported that HPV had not been recommended.