One hundred sixty patients with idiopathic scoliosis treated with Cotrel-Dubousset instrumentation (CDI) underwent preoperative and postoperative sagittal plane analysis of the thoracic spine, thoracolumbar junction, and lumbar spine. The data suggest that mild to moderate improvements in thoracic hypokyphosis are possible. When crossing the thoracolumbar junction, reversal of rod bend and reversal of hooks on the derotation rod appear to provide the most physiologic sagittal contour. Cotrel-Dubousset instrumentation to the mid and distal lumbar spine can preserve and, at times, enhance lumbar lordosis.