This paper documents a novel technique to estimate the inter-vertebral motion and related coupling in five patients with idiopathic scoliosis and five control subjects. Triads were put over the spinous processes of the subjects. An eight 60-200Hz video camera Motion Analysis Expert Vision System was used to track these markers for right lateral bend trials. The markers’ 3-D coordinates were reconstructed by means of the Direct Linear Transformation technique after camera calibration. Rotations between any two triads were estimated by the Euler angles in the following sequence: bending, rotation and flexion. For a right bend, there is a left rotation of the thoracic spine and a compensatory right rotation of the lumbar spine in both the scoliotic spine and control subjects. Though, peak values were smaller for the scoliotic group but not significantly different, individual ratios involving the thoracic spine were significantly smaller for the scoliotic group denoting spinal rigidity.