We measured bone mineral content (BMC) with single photon absorptiometry in two groups of young patients with type I diabetes: the first group (prospective study) consists of 48 patients followed from onset to the third year of diabetes and the second group (cross-sectional study) consists of 66 long-term diabetics. Bone mineral content at onset of disease was lower than normal in only two cases. After 3 years of diabetes no male revealed BMC below the normal range but two females (6.6%) had low BMC values. In our cross-sectional study we found a BMC reduction in 12% of the cases. We did not find a relationship between bone deficit and duration of diabetes, or bone mass values and HbA1.