The development of scoliosis in animal models with induced asymmetric rib growth suggested the possible role of asymmetric rib growth in the etiopathogenesis of adolescent idiopathic scoliosis (AIS). Asymmetric rib length is well recognized in idiopathic scoliosis, however, whether this rib asymmetry was primary or secondary has not been clearly documented. We measured the lengths of all ribs in 48 patients with AIS and 29 patients with scoliosis associated with syringomyelia and Chiari I malformation (SS). In both groups, ribs on the concave side were significantly longer than those on the convex side in apical area. The rib length difference was significantly associated with magnitude of the Cobb angle of thoracic curve. However, the rib length discrepancy showed no difference between AIS and SS group. The finding of similar asymmetry of rib length in both AIS and SS patients with thoracic curve indicated the discrepancy found in AIS might be secondary to the spinal deformity rather than its etiological factor.