Investigations on the occurrence of mottled enamel due to fluoride intake were carried out in 274 children (7–12 years) in Cuban districts with different fluoride concentrations in the drinking water. A correlation between the fluoride concentration in the drinking water could be established both for the prevalence of caries and for frequency and severity of mottled enamel. Although the mean maximum temperature is 83.8 °F (28.8 °C), there was no objectionable dental fluorosis up to 1.6 ppm fluoride in the drinking water. Considering the caries reduction observed in different areas of this country, the climatic conditions in Cuba seem to require a caries-protective concentration of between 0.8 and 1.0 ppm fluoride.