The prediction of normal spirometric values requires a measure of the non-deformed body height of scoliotic patients. The arm-span method has been used for estimating the non-deformed body height in spite of the fact that opinions about the normal relationships between body height and arm span differ. In order to minimize the error of estimation of non-deformed body height, the normal relationships between body height and arm span were determined for 91 males and for 118 females of ordinary body stature, varying age (5-78 years), and Swedish origin. The body-height/arm-span relationships were described by linear regression equations taking age into account. The results indicate significant sex and age differences in the arm-span/height ratio. Multiple regression equations including arm span and age as regressors were used to calculate the non-deformed body height in scoliotic patients. The arm-span method was compared with the method using the degree of lateral curvature of the spine for calculation of non-deformed body height of scoliotic subjects. The arm-span method resulted in a correction of body height and predicted spirometric values that agreed closely with those obtained by the method using the degree of curvature of the spine. The two methods may be used alternatively. In accordance with earlier reports, the predicted spirometric values were underestimated when the measured body height was used.