Twenty-one adults who had a fracture of the middle of the humeral shaft and an injury of the ipsilateral brachial plexus were followed for an average of twenty-eight months. Only two of these patients showed evidence of neurological improvement. Of the eleven patients who had an associated traumatic injury to the brain, eight were treated non-operatively and three, operatively. The presence of a fracture of the humerus in a flail extremity has been found to delay rehabilitation markedly and to result in prolonged hospitalization. Eleven fractures were treated non-operatively with a brace or cast, and there were five non-unions, two delayed unions, and two malunions. Of the ten fractures that were treated operatively, three that were treated by compression-plating all united. Two fractures were treated by external fixation; one had a delayed union and one, a malunion. In the remaining five patients, who were treated with an intramedullary rod, there were two non-unions, one delayed union, and one malunion.