Fluorosis levels and caries prevalence were evaluated in 182 adolescents aged 15-16 yr residing from birth in an area with 5 ppm fluoride in the drinking water. The mean number of surfaces affected by caries in the total study population was 5.46 DMFS. The teeth most susceptible to caries were the first molars. The prevalence of fluorosis was 100% with 53 subjects demonstrating mild fluorosis (according to Dean's index), 83 demonstrating moderate fluorosis, and severe fluorosis diagnosed in 46 subjects. A statistically significant positive association was found between caries prevalence and fluorosis; the more caries experienced, the more severe the fluorosis level. Boys experienced significantly higher fluorosis levels than girls. Further research will investigate the possible variables which may explain this difference in fluorosis by sex.