The aim of this study was to assess teens' knowledge of HPV infection and vaccination one year after the initiation of the public vaccination programme and information campaign on the disease and the opportunity of vaccination. Between 15 May and 15 June 2009, a survey was carried out on 1,105 teenagers attending high schools in a town in the northeast of Italy by means of an anonymous and unannounced questionnaire covering the knowledge of HPV infection, transmission, prevention, vaccination and post-vaccination behaviours. Only 75% of teens knew what HPV infection is (92% of girls vs 51% of boys, p < 0.001); only 70% knew that it is a sexually-transmitted infection. Only 69.3% associated condoms with HPV disease prevention (72.6% girls vs 61.5% boys, p = 0.002). About 18.8% of girls and 33.2% of boys believe that HPV can lead to AIDS (p < 0.001). Among teens aware of HPV vaccination, 7.6% of girls and 21.8% of boys believe that it can prevent AIDS (p < 0.001). Only 75.5% of girls and 51.1% of boys (p < 0.001) believe that condom use remains useful for HPV prevention after vaccination. The need for regular pap smears after vaccination is reported by 93.3% of girls. Teens' knowledge about HPV infection and vaccination remains insufficient, despite a broad information campaign. Erroneous information may increase risky sexual behaviours. Without complete information about HPV infection and vaccination and information about other sexually-transmitted diseases, the latter might become difficult to control among teenagers, while some misunderstandings about the usefulness of secondary prevention might linger.