Dental caries is the most common oral disease seen in children and adolescents. This study was conducted to assess prevalence of dental caries at different water fluoride levels in Nalgonda district of Andhra Pradesh. A total of 1800 school children aged 12-15 years were selected by stratified cluster sampling from three areas with different levels of natural fluoride concentrations in drinking water. Water samples were collected and analyzed for fluoride concentration. Dental caries was recorded using Dentition Status and Treatment Need index. The overall prevalence of dental caries in the study population was 35.2% and the remaining 64.8% of the children were caries free. The prevalence of caries in below optimal was the highest (57%) followed by above optimal fluoride areas (33.3%). The lowest prevalence of caries was found in the optimal fluoride areas (17.2%). The difference in the prevalence of dental caries between different fluoride areas was statistically significant. The prevalence of dental caries was more in below optimal fluoride area followed by areas where fluoride concentration was 5ppm and above. The lowest caries prevalence was found in optimal fluoride areas. There was a positive correlation between severity of dental fluorosis and prevalence of dental caries. There was a negative correlation between fluoride concentration and dental caries. The prevalence of dental caries decreased with increasing concentration of fluoride in the drinking water up to 5 ppm.