The prevalence of dental fluorosis, a manifestation of chronic fluoride toxicity on ameloblasts, is increasing in communities with or without fluoride supplementation of drinking water. The aim of this work was to study the prevalence and severity of fluorosis in Chile and its relationship to socioeconomic level and fluoride content of drinking water. Six hundred ninety three children aged 7 to 12 years old, coming from four cities with drinking water fluoride levels of 0, 0.3, 1 and 2.2 ppm were subjected to a standardized odontological examination looking for clinical manifestations of fluorosis. The global prevalence of fluorosis was 32%, being 61.4% in the city with the highest drinking water fluoride concentration and 20% in the city without fluoride in the drinking water. Likewise, the prevalence of fluorosis was higher in children of high socioeconomic level. It is concluded that the high prevalence of fluorosis, although generating only mild lesions, should be object of epidemiological surveillance.