Bone histomorphometry was carried out in 11 women, aged 53 to 80 (mean = 69.6), treated with fluoride for vertebral osteoporosis for more than 6 months and having suffered one or more stress fractures (1 to 4 sites, mean = 1.7 sites) during that time. Classical contraindications were complied with in all cases but 2 patients did not have any combined calcium supplement. In 6 cases, histomorphometry showed no sign (notably hyperosteoidosis) of the effects of fluoride on bone. Bone trabecular volume was markedly below the fracture threshold in 4 patients. This group refractory to fluoride included the two patients who had received no calcium supplement. In 5 cases, histomorphometry showed hyperosteoidosis of normal or low thickness, with a normal mineralisation rate, reflecting the effects of fluoride on bone. However, bone trabecular volume remained below the fracture threshold in all cases. In all 11 cases, bone structure studied in polarised light was lamellar and there was no increase in cortical porosity. These results suggest that the imputability to fluoride of peripheral bone accidents must be viewed very relatively (the persistence of an insufficient bone trabecular volume being the feature usually found) or, at any event, that its possible iatrogenic effect is not linked to bone remoulding abnormalities.