Objective: The aim of this study was to investigate the caries prevalence of children living in either low- or high-fluoride areas and to relate caries experience to the severity of dental fluorosis. Method and materials: A total of 278 12- to 14-year-old schoolchildren, 149 in a low-fluoride area (LFA) and 129 in a high-fluoride area (HFA), were included in the study. The naturally occurring fluoride concentrations in the drinking water were 0.30 to 0.40 ppm in the LFA, 1.42 to 1.54 ppm in the HFA1, and 1.55 to 1.66 ppm in the HFA2. Dental caries was recorded with the World Health Organization criteria, and dental fluorosis was measured using the Tooth Surface Index of Fluorosis. Results: The percentages of children who had an average TSIF greater than or equal to 1 were 0%, 29%, and 77% in the LFA, HFA1, and HFA2, respectively. The mean decayed, missing, and filled permanent teeth (DMFT) and decayed, missing, and filled permanent surfaces (DMFS) were 0.84 +/- 0.98 and 1.58 +/- 2.24 in LFA, 1.30 +/- 1.46 and 1.78 +/- 2.52 in HFA1, and 1.26 +/- 1.42 and 1.97 +/- 2.60 in HFA2, respectively. There was no significant difference in caries prevalence among children living in low- and high-fluoride areas when evaluated with an analysis of covariance model, including the frequency of toothbrushing. Toothbrushing frequency had a significant effect on the decayed teeth, decayed surfaces, DMFT, and DMFS. In high-fluoride areas, there was no relationship between caries prevalence and severity of fluorosis. Conclusion: Increasing water fluoride levels were associated with higher prevalence and severity of dental fluorosis and had no influence on caries experience in children with poor oral hygiene.