The prevalences of dental caries and developmental enamel defects were assessed in 643 randomly selected children aged 11 to 13 years who were lifelong residents of three areas of Naples with high (4 ppm), optimal (1 ppm), and low (0.3 ppm) concentrations of fluoride in their drinking water. The children living in the high fluoride area had significantly lower dental caries scores (DMFT 0.59, DMFS 1.01) than those in the optimal fluoride area (DMFT 1.67, DMFS 2.87) and those in the low fluoride area (DMFT 1.97, DMFS 3.48). The FDI index of developmental defects of dental enamel (DDE) was used to record enamel defects. There was a significant increase in the number of children with at least one tooth affected by an enamel defect as the fluoride level in their drinking water increased; the prevalences were 9.8 per cent in the low fluoride area, 23 per cent in the optimal area and 53.1 per cent in the high fluoride area. The prevalences of teeth affected were 2.2 per cent in the low fluoride area, 5.7 per cent in the optimal, and 20.3 per cent in the high. Demarcated opacities were the most common defect seen. Diffuse opacities were found to be the discriminating factor between fluoride and non-fluoride areas. In the high fluoride area 64.3 per cent of children with enamel defects had at least six teeth affected. In the maxilla the central incisors were the most affected teeth followed by the second and first premolars; in the mandible the first premolars and first molars were the most affected teeth.