SUMMARY PURPOSE To analyze the level of knowledge about and the acceptability of the HPV vaccine among vaccinated and unvaccinated adolescents in the Western Amazon. METHODS A cross-sectional study on adolescents aged 10 to 19 years. The instrument used to collect data contains demographic and socioeconomic information and 27 questions that assess the knowledge and acceptability of the HPV vaccine. To compare the prevalence of vaccinated adolescents with the correct answers to questions about HPV and acceptability and vaccination, the robust variance Poisson regression model was used in the Stata 13.0 software. FINDINGS A total of 190 adolescents participated in the study, 60.5% in the age group of vaccination recommended by the Brazilian government, among them, 53.9% reported not having been vaccinated (p <0.001). A total of 150 (78.9%) adolescents correctly recognized HPV as a virus; 121 (63.7%) recognized HPV as a cause of cervical cancer. Participants who know HPV is a causative factor for cervical cancer are 1.94 times more likely to have been vaccinated than those who do not. Among the interviewees, the main sources of knowledge about the vaccine were schools (51.6%) and health professionals (22.6%). CONCLUSION Unvaccinated adolescents have knowledge gaps about HPV and its vaccine when compared to those vaccinated. Our results emphasize the need for effective campaigns to deliver adequate information about HPV and its vaccine to adolescents, their parents, and health professionals.