Introduction: Caries and periodontal diseases are the most common infectious diseases that affect the human being. Currently in Chile, caries has a high prevalence and constitutes an important public health issue. Therefore, in 2015 the Integral Dental Attention Program was introduced for fourth-year secondary school students. Objective: to determine the prevalence of caries in the Trehuaco and Lota communes in fourth-year secondary school students. Materials and methods: the selected population consisted of teenagers from the Integral Dental Attention Program for fourth-year secondary school students at public and semi-private schools, with a total universe of 114 teenagers, 70 of which belong to the Lota commune. Clinical records were analyzed to obtain the variables, which were DMFT index, FONASA (public health insurance) coverage level, medical records and sex. Results: DMFT value was 6.2 for teenagers from Trehuaco and 5.41 for teenagers from Lota; 4.9 for men and 6.7 for women; 5 for the D coverage level of FONASA and over 6.86 for the other levels. Conclusion: Caries prevalence was higher in teenagers from the Trehuaco commune. Regarding sex, female teenagers were more affected. Likewise, regarding FONASA coverage level, the more affected were those from the A, B and C levels.