To date, all the authors who have recommended external rotation osteotomy (ERO) in the late treatment of obstetrical brachial plexus palsy (OBPP), have neglected upper limb length discrepancy, which is an another sequelae of OBPP. In this paper, a new technique is reported for the late treatment of OBPP patients with upper limb length discrepancy, in which both humeral external rotation osteotomy (ERO) and lengthening are applied with an intramedullary elongation nail. With this technique, upper limb function is improved through re-orientation of the shoulder arc to a more functional range, and further improvements will be seen in the appearance of the upper limb with the elimination of length discrepancy. It is also advocated that there is a potentiating effect of the humeral lengthening on shoulder movements gained by ERO when the osteotomy is applied above the deltoid insertion, as this allows more lateralized placement of the deltoid insertion. (c) 2017 Turkish Association of Orthopaedics and Traumatology. Publishing services by Elsevier B.V.