In order to determine if the configuration of the trunk is altered when a patient changes from an upright to a forward-bending position, the shape of the surface of the back of fifty-six patients who had adolescent idiopathic scoliosis was recorded, by means of Raster stereophotography, with each patient in three postures: standing erect, bending forward with the hands between the knees (forward bend 1), and bending forward with the hands touching the toes (forward bend 2). The effect of placing one foot on a block to produce a limb-length difference was also studied in the standing position (thirty patients) and in the forward-bending position (eighteen patients). The degree of rotation of the surface of the back and of kyphosis and lordosis of the surface of the trunk was measured from sections in the sagittal plane that were plotted from the computerized measurements of the surface of the back. Qualitatively similar rotation of the surface of the back was found in both the standing position and the forward-bending position. When the patient was in the forward-bending position, the degree of rotation of the surface of the back was minimally changed in the thoracic region but increased in the lumbar region. The amount of rotation of the surface of the back was similar in both forward bending with the hands to the knees and forward bending with the hands to the toes.(ABSTRACT TRUNCATED AT 250 WORDS)