Objective: To determine the caries and fluorosis prevalence of adolescents in 3 communities in Iran with varying urbanization and concentrations of fluoride in the piped water. Method and Materials: Data were obtained from 593 examinations of 12- and 15-year-olds in Tehran (water fluoride concentration: 0.3 mg F/L), the city of Semnan (1.3 mg F/L), and the village Dibaj (0.2 mg F/L) in Iran. Results: In both age groups, comparable counts of decayed, missing, and filled surfaces (DMFS) were observed, whereas the values related to teeth (DMFT [SD]) were significantly higher in 12-year-olds from Semnan (1.5 [1.8]) than those for children from Dibaj (0.7 [1.0]) (P .05; Mann-Whitney test) but comparable to those for children in Tehran (1.2 [0.7]). A lower prevalence of dental restorations was reported for both Semnan and Dibaj (Unmet Restorative Index [UNT]: 67% to 82%) compared to Tehran (15% to 39%). In Semnan, the risk of having medium to severe fluorosis was 10- and 34-fold compared to Tehran and Dibaj, respectively. Conclusions: Caries prevalence was relatively low compared to that in other countries in the Middle East. In the examined population, which was not adjusted to socioeconomic status, naturally fluoridated water seemed to have no obvious effects on DMFT, but resulted in an esthetically relevant higher prevalence of dental fluorosis. Schlagwörter: caries prevalence, fluorosis prevalence, epidemiology, Iran, Middle East, water fluoridation