Iliac crest biopsies were taken from patients with hip fracture from a low-fluoride area (less than 0.3 ppm), from an area with fluoridated drinking water (1.0-1.2 ppm), and from a high-fluoride area (greater than 1.5 ppm). Fluoride content analysis and histomorphometry of bone were performed. The hip fracture incidence during 1972-1981 was studied in the same areas. The fluoride content of the bone samples correlated with drinking water fluoride. In patients with hip fracture, both osteomalacia and osteoporosis were common. In the high-fluoride area also osteofluorosis was found in many patients. Osteofluorosis may occur if the fluoride content of trabecular bone exceeds 4,000 ppm and either the volumetric density of osteoid or the osteoid-covered trabecular bone surface is abnormally increased. There was no difference in incidence of hip fracture in the three areas.