The aim of this study is to simplify the distal radius and ulna classification for practical use and to test its reliability. This was a prospective single-center study of patients with juvenile and adolescent idiopathic scoliosis. Left-hand radiographs were retrieved for measurements by three examiners. Reliability analysis was carried out by intraclass correlation. 34 females and 16 males were recruited, mean age 12.7 years (±SD 1.7). The grades varied from R4-R11 to U1-U9. There was strong to near-perfect intraclass correlation. This study concludes that the simplified distal radius and ulna classification is a reliable tool for assessment of skeletal maturity.