Idiopathic scoliosis leads to a three-dimensional thoracic deformity. The purpose of this study is to measure thoracic dimensions and volume related to growth and to verify the influence of moderate and severe scoliosis. 176 children (36 boys, 140 girls; 4–16 years) with scoliosis <45 degrees and 17 patients (2 boys, 15 girls) with scoliosis >65 degrees were compared to 239 children without spinal deformity (97 boys, 142 girls) using an optical system. Thoracic volume, perimeter, anterior-posterior and transversal diameters, T1–T12 and sternal lengths were calculated. These measurements were related to age and sitting height. Thoracic volume (3–16 dm3) did not differ significantly over growth between reference and moderate scoliosis groups. At 4 years, it represents 33%, at 10 years it represents 55% of its volume compared with age 16. It triples from 4–16 years and doubles during puberty. In severe scoliosis, the age related thoracic volume was always lower than volumes in reference and moderate scoliosis groups. During growth, the transversal diameter corresponds to 30%, the anterior-posterior diameter represents 20% and the thoracic perimeter 100% of sitting height. In severe lordoscoliosis the anterior-posterior diameter represents less than 20%. Scoliosis <45 degrees does not influence thoracic volume significantly. Severe deformities seem to inhibit volumetric growth. Thoracic parameters should be related to growth parameters such as sitting height rather than age because of possible height variations in one age section. The established relationships offer a reliable orientation of thoracic proportions. They help to understand the global deformity and represent a baseline for surgical treatment using vertical expandable prosthetic titanium ribs.