Accurate noninvasive measurements of spinal curvature are crucial in planning treatment and assessing curve progression in adolescent idiopathic scoliosis. An inter-rater agreement trial and an intra-rater agreement trial were undertaken to estimate the reliability of axial rotation measurement using the Scoliometer (Orthopedic Systems, Inc., Heywood, California). In the Inter-rater trial, two orthopedic surgeon measured the thoracic and lumbar axial rotations of 22 patients with idiopathic scoliosis using the Scoliometer. In the intrarater, trial a single orthopedic surgeon measured the thoracic and lumbar axial rotations of 25 patients on four separate occasions with the Scoliometer. Inter-rater agreement using Scoliometer to estimate the magnitude of the hump (in centimeters) in the thoracic and lumbar regions was poor (intraclass correlation coefficient Rho = 0.57 a nd Rho = 0.76 for thoracic and lumbar regions, respectively). Inter-rater agreement using the Scoliometer to estimate the degree of axial trunk rotation was better (Rho =0.81 and Rho = 0.82 for the thoracic and lumbar regions, respectively). Intra-rater agreement using this device to estimate the magnitude of the hump (in centimeters) in the thoracic and lumbar regions was good (Rho = 0.90 and Rho = 0.84 for the thoracic and lumbar regions, respectively). Intrarater agreement using the Scoliometer to estimate the degreas of curvature was outstanding (Rho = 0.995 and Rho = 0.998 for the thoracic and lumbar regions, respectively). These results indicate that the Scoliometer can be a reliable noninvasive method for respectively assessing spinal axial rotation when used by a single trained observer.