There have been few reports of actual measurements of rib length in patients with idiopathic scoliosis. We measured the lengths of the 7th to 12th ribs in 28 patients with idiopathic scoliosis with right convex single thoracic curve. The measurements were performed by the multi-projection volume reconstruction method of computed tomography. A significant difference between the left and right side length (laterality) was observed in the 11th and 12th ribs. Laterality was not observed in the 7th, 8th, 9th, and 10th ribs. In this study, it appeared inadequate to conclude that the laterality of rib length caused the scoliosis. Since the 11th and 12th ribs were floating ribs, we speculated that, on the contrary, the scoliosis affected the laterality of the rib length.