Fourteen-year-old boys from three regions of Saudi Arabia were surveyed in 1992/3. These regions were Jeddah (which receives desalinated water containing 0.22 mgF/l), Riyadh (receiving water containing 0.78 mgF/l) and Qassim (2.66 mgF/l). For each of these urban communities an adjacent rural community was selected; these received water with 0.25, 0.80, and 2.71 mg/l, respectively. Subjects from the urban communities were classified into high, medium and low socio-economic status based on area of residence, income and education level of parents. Nutritional status was calculated from height and age using WHO methods and expressed as height for age percentage of the median of the reference population (HAM); children with HAM scores of less than 95% were classed as malnourished. The developmental defects of enamel index was recorded on the buccal surface of all permanent teeth, by one examiner. Colour photographs of anterior teeth were read 'blind' to investigate examiner bias between regions-there was no bias. A total of 1,539 children were examined who had been continuously resident in that community. Overall, 83% of subjects had one or more enamel defects with a mean number of teeth affected per person of 9.6. Diffuse defects were the most common. Multivariate analyses revealed that all three variables-region, nutritional status, socio-economic status-were statistically significantly related to the prevalence of defects and the number of teeth affected: prevalence was highest in the region with the highest water fluoride concentration, in rural areas and in malnourished subjects. Maxillary incisor teeth were the most affected teeth in all regions. The findings have implications for those in public health who determine optimum fluoride levels in drinking water in Saudi Arabia and beyond.