Background: Prophylactic human papillomavirus (HPV) vaccines are available, but uptake is suboptimal. Information on factors influencing parental decisions regarding vaccination will facilitate the development of successful interventions.Methods: Parents of girls ages 9 to 17 years (n = 476; cooperation rate = 67%) from a panel of U.S. households completed online surveys between September 2007 and January 2008, documenting vaccine knowledge, attitudes, and intentions.Results: Among those aware of the vaccine, 19% had already vaccinated their daughter(s), 34% intended to, 24% were undecided, and 24% had decided against vaccination. Awareness of HPV was high but knowledge levels were suboptimal (mean 72%, SEM 0.8%). Black and Hispanic parents were significantly less likely to be aware of the vaccine compared with White parents. In multivariate analyses, compared with parents who opposed vaccination, those who had already vaccinated their daughter(s) or who intended to do so had more positive attitudes, reported fewer barriers, and were more likely to perceive that family and friends would endorse vaccination. They also reported higher levels of trust in pharmaceutical companies that produce the vaccine.Conclusions: Despite limited knowledge, most parents had decided to vaccinate their daughter(s). Given evidence of diminished access to information among Black and Hispanic parents, programs should focus on reaching these groups. Interventions should address parental concerns about behavioral consequences, reduce structural barriers, and promote the perception that vaccination is endorsed by significant others. Moreover, interventions may need to address mistrust of pharmaceutical companies.Impact Statement: This study documents factors associated with parental decisions about HPV vaccination for their daughter(s) and provides direction for intervention development. Cancer Epidemiol Biomarkers Prev; 19