High-risk human papillomavirus (hrHPV) is the 2nd leading cause of cancer in women Bivalent Cervarix™ vaccine is highly efficacious against hrHPVs and associated precancers. Mathematical models disagree about the best vaccination strategy. Thus, we established a community randomised phase IV trial (CRT) to assess effectiveness of different vaccination strategies. During two school years (2007–8 and 2008–9) 80 000 1992–1995 born boys and girls were invited to participate in a CRT in a total of 33 communities in Finland. In 11 arm A communities 90% of girls and boys received HPV16/18 vaccine, in 11 arm B communities 90% of girls received HPV16/18 vaccine and boys received hepatitis B-virus (HBV) vaccine, and in 11 arm C communities both girls and boys received HBV vaccine. Effectiveness of the vaccination strategies in terms of reduction of hrHPV rates was assessed in vaccinated and unvaccinated 18.5 year-old girls. Recruitment resulted in equal enrolment of four birth cohorts (born 1992–95) comprising altogether 32 176 (approximately 40% response) adolescents, including 22 514 girls (> 50% response per birth cohort and arm) and 11 651 boys (20–30% response per birth cohort and arm). Already completed follow-up of 3 614 and 3 256 1992 and 1993 born girls at the age of 18.5 years prove that cervical samples from 350 vaccinated and 85 unvaccinated girls by community will be available. Assuming 80%–95% vaccine efficacy and 30%–50% effectiveness we have 80%–90% power to identify differences between vaccination strategies. In conclusion, this phase IV CRT augments decision making how to implement HPV vaccination programmes.