Background. The present study aimed to determine the prevalence of and relationship between dental caries and dental fluorosis at varying levels of fluoride in drinking water. Methods. The study was conducted among 3007 school children in the age group of 12 to 16 years in 2 districts of Haryana having varying fluoride levels in drinking water. Type III examination for dental caries according to the WHO index and dental fluorosis estimation according to Dean’s index was done. Results. The prevalence of dental caries decreased from 48.02% to 28.07% as fluoride levels increased from 0.5 to 1.13 ppm, but as the fluoride level increased further to 1.51 ppm, there was no further reduction in caries prevalence, but there was a substantial increase in fluorosis prevalence. Conclusion. The optimum level of fluoride in drinking water was found to be 1.13 ppm, at which there was maximum caries reduction with minimum amount of esthetically objectionable fluorosis.