PURPOSE: To evaluate and report the clinical and radiological results of the intramedullary fixation by retrograde flexible nail in the humeral shaft fracture. MATERIALS AND METHODS: From July 2002 to May 2005, seventeen cases who had the humeral shaft fracture were treated with the intramedullary fixation by retrograde flexible nail. Fifteen cases were followed up and the clinical and radiological results were analyzed. RESULTS: All of the cases had satisfactory fracture union, and none of the patient had limitation in shoulder or elbow joint movement, and shoulder or elbow joint pain, and average ASES was 42.86 point. There was 1 case of delayed union, and 3 cases of distal nail displacement. Another severe complications were not occurred. CONCLUSION: Intramedullary fixation by retrograde flexible nail is one of the effective method in the humeral shaft fracture without nerve or vessel injuries, and also can avoid the complication of wide soft tissue incision or rotator cuff injury.