BACKGROUND The multifactor aetiology of adolescent idiopathic scoliosis is commonly acknowledged. Both multivariate analyses of large study groups and the search for causes of adolescent idiopathic scoliosis and its progression in individual patients indicate that the aetiopathogenesis of this disorder is remarkably complex. The discovery of novel bone turnover markers, such as Klotho protein and FGF-23, means that their role in this condition also has to be considered. The aim of this paper is to evaluate the FGF-23 and Klotho protein concentration profiles as new contributors to the regulation of calcium and phosphate metabolism in children with adolescent idiopathic scoliosis and compare them with the values seen in healthy children. METHODS The study assessed a total of 70 children, including 35 children treated at the postural defects clinic of the Health Care Facility in Oleśno following a diagnosis of adolescent idiopathic scoliosis and 35 healthy children who constituted a control group. The levels of classic bone turnover markers, such as calcium and phosphorus concentration, alkaline phosphatase, 25-OH-D, and parathyroid hormone (PTH) activity, and of newly discovered contributors to calcium and phosphate metabolism regulation, namely Klotho protein and FGF-23, were determined in both groups. RESULTS There were statistically significant differences in the levels of basic parameters of calcium and phosphate metabolism between children with scoliosis and the control group, with scoliotic patients showing elevated calcium and 25-OH-D levels and reduced parathyroid hormone levels. Klotho protein levels in children with scoliosis were significantly lower than in the control group. Moreover, the scoliotic patients showed a marked trend towards higher FGF-23 levels as compared to the control group. CONCLUSIONS 1. Adolescent idiopathic scoliosis is characterised by multi-level abnormalities of calcium and phosphate metabolism. 2. The increased FGF-23 levels and reduced Klotho protein concentrations found in serum samples collected from children with ado-lescent idiopathic scoliosis may suggest that these hormones play a role in the aetiopathogenesis of the disorder.