The introduction of reliable and non-invasive methods of measuring bone mass has allowed investigators to study the bone mass loss (ostopenia) related to rheumatic diseases and corticosteroid therapy. Serial measurements of lumbar bone mineral density (BMD) by dual-photon absorptiometry (DPA) is an effective method of checking bone mineralisation. In children, however, the bone mass is not constant over time, so bone densitometric measurements must take into account not only the net loss but also the missing increase in BMD. In order to study the effects of both chronic rheumatic disease and the long-term administration of corticosteroids in children, as a first step the reference curves of bone mineralisation (mean BMD values and annual % BMD growth rates) were calculated from a control population of 79 children (32 males and 47 females) aged 3 to 20 years. All the subjects involved in the study underwent DPA utilising a Norland Bonestar instrument provided with a 153 Gadolinium source and the average BMD (g/cm2) of the lumbar spine was calculated. As a second step, a transverse study was carried out on a series of 157 children and young adults affected by chronic rheumatic diseases with juvenile onset. As a third step, a longitudinal study on the adverse effect of the chronic administration of corticosteroids on bone mineralisation was carried out on a series of 58 patients affected by chronic rheumatic diseases with juvenile onset who were being treated with long-term corticosteroids. Serial measurements of bone mass should help us to improve our strategies in preventing and counteracting osteopenia due to the chronic administration of corticosteroids also in children.