The efficacy of fluoride in the community drinking water for the prevention of dental caries has been well established. The average daily intake of fluids in normal children varies with age, sex, temperature and season. Children with polydipsia as in nephrogenic diabetes insipidus consume excessive quantities of water. We are reporting two children with nephrogenic diabetes insipidus and fluorosis, and suggest looking for evidence of fluoride toxicity in individuals with polydipsia. Substituting nonfluoridated water as part of the fluid intake is recommended.