The amount of correction from spine deformity surgery that is required to avoid asymmetric and unbalanced sifting is not known, and methods sensitive enough to document moderate changes in pressure distribution over time are few, as the commonly used methods are qualitative or semiquantitative. The aim was to analyse seating pressure distribution with a pressure sensor mat system in patients with nonidiopathic scoliosis and to compare the pressure distribution with that in able-bodied controls. The aim was also to apply the method in a surgically treated scoliosis group before and after the spine fusion. Peak pressure, contact area of the entire and the maximum pressure surface, and three measures of asymmetry were calculated. Patients had higher peak pressure and more asymmetric loading than controls. Significant difference was indicated in contact area. After the spine fusion, all asymmetry indices improved. The method fulfilled clinical needs to detect the differences from normal controls as well as the surgery-dependent changes.