Preliminary costectomy before Harrington instrumentation and fusion for idiopathic scoliosis allows direct excision of the rib prominence and better correction at the second-stage operation. The excised rib fragments are used as grafts, thus avoiding the need for a separate pelvic incision. The management regime and the technique of costectomy are described. The results in 42 children, most suffering from adolescent idiopathic scoliosis and all treated by this method, have been reviewed. Respiratory function in a group of these children has been compared with that of a group treated by Harrington instrumentation alone. Costectomy produced a significantly greater reduction in total lung capacity and peak expiratory flow rate but, providing the preliminary lung function tests were reasonably normal, the cosmetic and psychological effects of costectomy were very rewarding.