The aim of this study was to evaluate the levels of receptor activator of nuclear factor kappa-B ligand (RANKL), receptor activator of nuclear factor kappa-B (RANK) and plasma osteoprotegerin (OPG) levels, in T1D youngsters and to investigate factors that could influence the OPG/RANK/RANKL signaling axis such as 25-hydroxy vitamin D [25(OH) D], parathormone (PTH) and age. The gene discussed is TNFSF11; the disease is type 1 diabetes mellitus.