The angle of abduction is an unsatisfactory guide in performing an upper femoral osteotomy. The use of the postosteotomy angle is suggested instead. This angle is measured by the line of the shaft and the line running from the upper end of the osteotomized shaft to the femoral neck. The postosteotomy angle represents the angle of the neck of the osteotomized femur. This angle should not be made greater than the angle of inclination of the outer wall of the level pelvis, unless limitation of hip motion is desired. The appreciation of the significance of this angle permits a logical understanding of the indications for the various types of upper femoral osteotomy.