We studied phosphorus and calcium metabolism in 50 adult insulin dependent and non insulin dependent diabetics arranged in 4 groups according to therapy and control of diabetes. We observed: a low level of blood magnesium in all diabetics a lower level of P T H, more pronounced with poorly controlled diabetes. a decrease of 1-25 (OH) 2 D levels without modification of the 25 (OH) D levels in badly controlled diabetics. This decrease may be related to the low level of PTH with a 1 alpha hydroxylation defect. These results are in favor of the hypothesis of a primary bone problem leading to the pre-senile and subclinical osteoporosis observed in diabetics. Hyperglycaemia rather than insulinopenia may be involved. Rigorous diabetes control significantly decreases all the observed differences, except the low magnesium level.