The parameters in adolescent idiopathic scoliosis correction (longitudinal height gain, coronal and sagittal plane changes) that correlate most closely with an increase in thoracic volume are reported. With pre- and postoperative radiographs of matched patients having straight Harrington distraction rods and contoured Luque rods, coordinates were digitized and the change in thoracic volume was calculated in ten subjects undergoing surgery for right thoracic curves. An increase in volume (7% increase in Harrington rod and 16% among Luque rod patients) was most closely correlated with a change in thoracic kyphosis toward physiologic ranges.