Introduction. Skeletal maturity assessment in Idiopathic Scoliosis (IS) is used for the evaluation of deformation progression risk, as well as selecting a method of treatment. The Sanders Maturity Scale (SMS) is based on the ossification of phalanges, metacarpal bones and radius rated on AP radiograms of the left hand. Aim. This retrospective study aimed to compare SMS to other skeletal maturity assessment methods used in daily practice. Materials and methods. We included 39 female patients with IS (50 series of radiograms) with a mean age of 13.4, ranging from 10.3 to 17.3. Each series of radiograms was evaluated by three observers with different experience. Skeletal maturity was assessed using the Sanders Maturity Scale (SMS), Risser sign, Greulich and Pyle (GP) atlas, as well as the closure of the triradiate cartilage. Results. The majority of patients, 17 out of 50 (34 %) were classified as type 3 (adolescent rapid – early). Intra-observer and inter-observer reliability for the SMS was very good (Krippendorff’s alpha >0.95). The GP and Risser method showed good reliability, whereas the triradiate cartilage closure assessment showed lower reliability. The Risser 0 grade corresponded with as many as four Sanders stages, 16 out of 20 (80 %) were rated Sanders 3. All radiograms with open triradiate cartilage (7/50, 14 %) were rated Sanders 2 or 3; they all received a Risser 0 grading. Conclusions. The SMS proved to have a very good intra-observer and inter-observer reliability, it is easy to be used by physicians and does not require an atlas. The SMS enhances the assessment of skeletal maturity of IS patients by providing additional stages in the early phase of growth (Risser 0).