Endemic fluorosis is widespread in the East African rift system, including the Ethiopian Rift Valley, where it is associated with highly fluoridated drinking water in areas of acidic volcanic rocks. Particularly tuff, pumice, obsidian, and ryolites in the younger basalts contain high concentrations of fluorite and fluorapatite. Fluoride levels in these areas are generally higher in groundwater than in surface waters, 1 posing a health risk to communities depending on wells for their drinking water. Fluoride concentrations between 1 ppm and 36 ppm have been reported from areas of endemic dental and skeletal fluorosis in the Ethiopian Rift Valley. 1 , 2 Recently, fluoride levels above the optimum and safe fluoride concentration of 0.8–1.0 ppm and even above the upper acceptable limit of 1.5 ppm set by WHO 3 were reported from highland and lowland localities outside the Ethiopian rift system, indicating that the fluorosis problem in Ethiopia is greater than earlier thought. Accelerated population movements into these endemic areas as part of resettlement programs, commercial agriculture and industrial development, and rapid urbanization require comprehensive assessment of the public health risk posed by fluoride and of appropriate and feasible control measures. A limit of 0.7 ppm has been recommended for hot climates, where water consumption by humans is highest. 4