Abstract A cross-sectional study in conjunction with a health extension program was conducted with 605 adolescents aged between 13 and 18 years from 22 public schools in Divinópolis, Brazil. The aim of the study was to determine the vaccination status of the adolescents and their level of knowledge of communicable and vaccine-preventable diseases. Three-stage cluster sampling was used comprising schools, classes, and students. The findings show that vaccination coverage among adolescents was 45.1% and yellow fever was shown to have the lowest coverage rate (64%). The most mentioned diseases when the adolescents were asked which vaccinations they had had were infantile paralysis (60.7%), yellow fever (56%), tetanus (34%), and measles (28.6%). Extension activities were conducted with 6,650 people, comprising vaccination (2,334 doses administered), aimed at expanding vaccination coverage, and health education activities with 2,839 adolescents directed at sexually transmitted diseases, family planning; and licit and illicit drugs. The study had a positive impact in terms of the expansion of vaccination coverage and the extension activities played an essential role in increasing the adolescents' knowledge of the themes addressed.