Fluorotic bone specimens obtained from the skeletons of two subjects with advanced fluorosis and from bone biopsies of other patients have been shown to contain deposits of bone on the surface which form an irregular sleeve of new bone and many exostoses. The cortical bone showed mottled and partially mottled Haversian systems with a large number of lacunae and enlarged canaliculi. The mottled Haversian system also showed large resorption tunnels. The lamellae of these osteons were disorderly and irregular and did not form complete rings. Cancellization of cortex was also seen, but osteoid tissue could not be demonstrated.