We measured simple and complex balance responses with a force plate stabiliometer in 70 adolescents: 50 with idiopathic scoliosis (IS) and 20 controls. In stable static balance positions, the two groups performed similarly, but when the visual and somatosensory systems were challenged simultaneously, the IS group had a significantly higher mean body sway than the controls. Within the IS group, children with mild, nonprogressive curves that had not been operated on were significantly more likely to maintain their balance when the visual and somatosensory systems were challenged simultaneously than those with curves > or = 40 degrees, who had had surgery, and who had more rapid progression of the curve. These findings suggest that adolescents with IS have normal balance in static, stable positions but are not able to perform as well as normal adolescents in sensory-challenged positions, particularly if they have a severe, progressive curve. Longitudinal studies are needed to determine whether balance dysfunction can be used to predict progression of the curve.