Patients with both severe mental retardation and severe physical disability, so-called "jushouji", often have scoliosis as one of the complications. The correlation between radiological findings of paraspinal muscles and progression of scoliosis was investigated by computed tomography (CT) in 15 patients. We took the CT of paraspinal muscles at the apical vertebral level in each patient, and measured the size of cross-sectional area and the CT value of paraspinal muscles of the both concave and convex side. There was no significant difference of the size of cross-sectional area of the muscles between the convex and concave side. The average CT value of the muscles was normal on the convex side, but abnormally lower on the concave side. Scattered low density areas were recognized in the fascicles of both sides like moth eaten appearance, which was speculated as fatty tissue. The CT value of remaining muscles was within normal range. The CT value on the concave side became lower as the degree of scoliosis progressed. The group who could not keep sitting position independently showed lower CT value on the concave side and had more severe scoliotic curves than the group who could sit independently or with slight support. From the above results, it may be concluded that the paraspinal muscles of the concave side become secondarily atrophic due to disuse, and may not be responsible for the progression of the scoliosis.