Nine children with chronic post-traumatic dislocation of the head of the radius were treated by an osteotomy of the ulna with over-correction of the angular deformity and with elongation of the bone. Satisfactory results were obtained in eight cases, the only poor outcome following a three-year delay between the initial injury and the reposition. The interosseous membrane of the forearm appeared to be the most important structure in maintaining the corrected position of the radial head.