The purpose of this study was to assess the caries prevalence of children living in areas with either 0.25 or 2.5 ppm fluoride in the drinking water, and to relate caries experience to the severity of dental fluorosis. The children, aged 6-16 years (mean 11.3 years), were lifelong residents of their rural villages. The severity of dental fluorosis in the maxillary central incisors, assessed by Deans index, was 1.4 +/- 0.9 (n = 59) and 2.3 +/- 0.9 (n = 65) in the 0.25 and 2.5 ppm areas, respectively. There was no significant difference in DMFT between children from the two areas (2.6 +/- 2.3 n = 59 versus 2.1 +/- 2.3, n = 65). In the low-fluoride area 75% of the children had decayed permanent teeth compared to 66% in the high-fluoride area. In the primary teeth, however, both the caries prevalence and the dmft were significantly lower in the 2.5 ppm area than in the low-fluoridearea. Stepwise, multiple, linear regression analyses, including all children, showed a significant effect of age on DMFT (30% of the variance explained), but no explanatory effect of fluoride in drinking water, severity of dental fluorosis, or gender. Regression analyses based on children in the 2.5 ppm area alone, showed significantly higher DMFT by increased severity of dental fluorosis. In children with a mixed dentition (n = 66), there was no association between caries in the primary and permanent teeth.