The epidemiological situation of decay evolves differently in the world. In industrialized countries, prevalence has declined significantly due to preventive measures, while in developing countries many studies have shown that caries was increasing. The aim of this study was to assess the state of dental health of schoolchildren aged 15 in Grand Comore (Comoros). This was a descriptive cross-sectional study on 15 year-old schoolchildren in colleges in Grande Comore who agreed to be examined. Four hundred schoolchildren were chosen by a stratified sampling weighted according to the area of living. Three groups of indicators of dental caries were used: the components D, M and F, the average DMFT and prevalence. The WHO modified questionnaire for the assessment of dental health was used to collect data; continuous data were compared by Student t test and qualitative ones by Chi-square test. Fifty two percent of schoolchildren were male and 63.5% lived in urban area. From the 888 teeth bearing the stigmata of decay, 83.2% were decayed, 12.5% missed and 4.3% filled. These components of DMF were associated with sex (p = 0.039) and not with area (p = 0.12). The 2.22 DMFT average was not associated with sex (p = 0.58) neither with area (p = 0.57). The caries prevalence was higher in rural than in urban areas (p = 0.001) and was not associated with sex (p = 0.61). These results suggest that schoolchildren need decay treatments. The dental programs will have much more success when they will be integrated into more comprehensive programs to promote schoolchildren health.