Intramedullary nailing has become the most popular fixation method in the treatment of the shaft fractures of long bones especially of tibia and femur because it affords most rigid fixation of fracture via closed method which makes early rehabilitation possible. Nowadays intramedullary nailing of the humeral shaft is being performed by many surgeons with good results. Newer implants and better surgical techniques are being developed, which suggests application of this method can be widened. Purpose of this study was aimed to define whether intramedullary nailing could be an effective method or not in the treatment of humeral shaft fractures by documenting the practical points in the application of intramedullary nailing of humerus, effectiveness in fracture healing, any complications or obstacles. We managed thirteen humeral shaft fractures with closed locked intramedullary nailing with distal fanning devices(Seidel nail) from March 1993 to April 1994. Average follow-up period was 14 months(12 months-18 months). The results were as follows; 1, Union of the fracture was obtained at average 12.9 weeks(9 weeks-20 weeks) postoperatively except one case of nonunion, in which case, union was obtained at postoperative 10 months finally. 2. Among the 13 cases, painful limitation of shoulder motion remained in 6 cases. This complication was more common in the cases with protruded proximal end of the nail. Above results suggest that locked intramedullary nailing seemed to be one of the useful method in the treatment of the humeral shaft fractures. However, destruction and irritation of shoulder by the nail was found to be a grave problem, and we found that further investigations should solve this problem.