The effect of drinking water fluoridation on the fluoride content of human bone, on cancellous bone strength and on the mineral density of bone was studied by analysing 158 autopsy samples of the anterior iliac crest from persons from two different areas. In the samples from the town of Kuopio, where drinking water has been fluoridated since 1959, the fluoride concentrations were considerably higher than in samples from the surrounding area where low-fluoride drinking water is used. The fluoride content of bones from Kuopio increased significantly with age, while considerably less change with age was found in samples from outside Kuopio. The highest fluoride content in bone ash was observed in women with severe osteoporosis. Cancellous bone strength measured by a strain transducer was statistically significantly higher in women with chronic immobilizing disease from Kuopio, compared with the corresponding group from outside Kuopio. No statistically significant differences in bone strength were found in men. There were no statistically significant differences in bone mineral density, as measured by gamma ray attenuation, between the samples from the fluoridated and non-fluoridated areas.