Abstract: Objective To investigate the prevalence of endemic fluorosis in the northwestern region of Shandong province and to provide scientific evidence for making strategies for the prevention and control of the disease.Methods Eleven counties were chosen to carry out the investigation of endemic fluorosis.The content of fluoride in drinking water and urine was determ ined with F-ionse lective electrode.Dental fluorosis of children aged 8 to 12 years was diagnosed with Dean's method and skeletal fluorosis were diagnosed with clinic exam ination and X-rays.Results The investigation was conduct in 17 water-miprovement villages of 11 counties,among which 12 villages(70.59%) had water fluoride content 1 00 mg/L,5 villages(29.41%) had water fluoride content> 1 00 mg/L and the highest water fluoride content was 4.46 mg/L.The investigation was also condcuted in 16 non-water improvement villages in 11 counties,among which 5 villages(31,25/%) had water fluoride content 1 00 mg/L,11 villages(68.75%) had water fluoride content > 1 00 mg/L and the highest water fluoride content was 4.09 mg/L.The total prevalence of dental fluorosis among the children was 51.51% (701/1.361).The index of dental fluorosis was 1.05 and the rate of dental damage was 6.25% (85/1.631).The urinary fluoride values above 1.40 mg/L were found in 60.86% (510/838) of the children,with the highest urinary fluoride concentration of 15.20 mg/L.The rate of skeletal fluo rosis among the adults older than 16 years were 2.49% (454/18.257) and 15.79% (3/19) with clinic and x-ray examination,respectively.The urinary fluoride values above 1.60 mg/L were found in 62.27% (406/652) of the adults,with the highest urinary fluoride concentration of 25.44 mg/L.Conclusion The endemic fluorosis is not effectively controlled and the preventive situation for endemic fluorosis control is still very severe in the northwe stern region of Shandong province.So preventive measures for endemic fluorosis should be strengthened.