A method is proposed, whereby the amount of compensation or decompensation of a scoliotic spine can be accurately measured by comparing the geometrical figures formed by lines drawn from the second to the ninth ribs on both sides. The normal outline of the chest is designated as a trapezoid and abnormal chests in scoliotics show geometrical variations from that outline. The correction of a scoliotic curve should tend to produce a geometrical outline of the chest, approximately of trapezoid type.