Two new cases of osteofluorosis are presented. They are attested by the existence of a bone X-ray densification, by histological lesions of hyperosteoidosis and a large increase in the fluorine content. One is a 61 year-old man who consumed 2.5 l a day of Vichy St-Yorre (a mineral water containing 8 mg of fluorine ions per litre) during 11 years; the other, an 86 year-old man who during 20 years took 500 mg of niflumic acid a day, a non-steroidal anti-inflammatory drug containing 3 fluorine atoms per molecule (i.e., 50 mg fluorine per 250 mg gellule). Both these hypertensive patients had severe renal insufficiency. These two observations serve as a reminder of the indispensable precautions to be observed when prescribing fluorine salts in the treatment of post-menopausal osteoporosis: at least the plasma creatinine level should be available in order to calculate the endogenous creatinine clearance and any possible supplementary intake of fluorine salts should be checked.