In October 2011, the Advisory Committee on Immunization Practices (ACIP) recommended the quadrivalent human papillomavirus vaccine (HPV4) for the routine immunization schedule for 11- to 12-year-old boys. Before October 2011, HPV4 was permissively recommended for boys. We conducted a study in 2010 to provide data that could guide efforts to implement routine HPV4 immunization in boys. Our objectives were to describe primary care physicians': 1) knowledge and attitudes about human papillomavirus (HPV)-related disease and HPV4, 2) recommendation and administration practices regarding HPV vaccine in boys compared to girls, 3) perceived barriers to HPV4 administration in boys, and 4) personal and practice characteristics associated with recommending HPV4 to boys.