The aim of the study was to describe the impact of hepatitis B vaccination and disease incidence in adolescents and young people 12 years after the launching of a mass hepatitis B vaccination of pre-adolescents in schools. Vaccination coverage was assessed using administrative and serological data. Infection trends were evaluated by means of seroepidemiological surveys. High levels of vaccination coverage and vaccine-induced immunity were achieved. The resulting low proportions of susceptible adolescents and young people have undoubtedly contributed to the substantial reduction in the prevalence of hepatitis B infection in the 15-24 years age group (0.9 per 100 in 2001 versus 9.3 per 100 in 1986) and in the reported incidence of hepatitis B cases (80% reduction). Over the last 3 years, the declining trend seems to have been halted, although 35% of cases reported during this period corresponded to immigrants.