The purpose of this study was to investigate the sagittal thoracolumbar spine posture as represented by the vertebral centroids and to identify their relative position to the whole body's line of gravity. A non-invasive method was used to calculate the thoracolumbar centroid curve within the sagittal plane from back skin profiles. Twenty-eight male and fifteen female adolescents, of 14 and 15 years of age, were evaluated. The vertebral centroid postures were varied but the females' curve was found to be significantly more posterior of the line of gravity than the males' curve (P < 0.05). Also, the degree of kyphotic curvature was significantly greater in the males than the females (P < 0.05). The posture assumed by the spine, as indicated by the kyphotic and lordotic curvatures, was found to have a significant correlation (r(2) from 0.71 and 0.51 respectively) with the cumulative centroid displacement of the line of gravity and with gender, as well as with height, mass and spine depth.