To determine the relationship between bone mineral content (BMC), 25-Hydroxycalciferol (25OHD) and zinc serum levels in young insulin-dependent diabetics, we performed photon absorptiometry on a poorly controlled group of 22 patients. Zinc, 25OHD and alkaline phosphatase were measured in fasting serum. Ca, P, Mg, glucose and cAMP were determined in serum and in 24 hours urine collection. The diabetic group showed a significant decrease in BMC (less than 0.001) with raised urinary excretion rate of calcium (p less than 0.001). On the other hand, serum levels of zinc and 25OHD showed a significant decrease (p less than 0.001, both). We found a positive and significant correlation between glycosuria and urinary excretion rate of calcium (r = 0.77; p less than 0.001) and negative one for 25OHD and urinary excretion rate of calcium (r = -0.77; p less than 0.001). We conclude that decreased zinc and 25OHD serum levels in poorly controlled insulin-dependent (Type I) diabetic patients, in addition to raised urinary excretion rate of calcium, as result of the osmotic diuresis, contribute to bone loss in these patients.