Purpose: To analyze the clinical and radiologic results of the shoulder arthrodesis in brachial plexus injury patients with flail upper extremity. Material and Method: From Aug 1978 to April 2008, 29 shoulders in 29 patients with brachial plexus injury with shoulder fusion, we evaluated 20 shoulders in 20 patients, more than 1 year follow up. The average follow-up period was 6.45years (range: 1year~24years). There were 13 men and 7 women, and the mean age at the time of trauma was 32.0years(2~65 years). The type of injury was a motorcycle accident in 11 patients, in car accident in 5, pedestrian accident in 3, and fall from a height in 1. The lesion of injury was root and trunk in 1 patient, trunk and cord in 1, trunk in 18. Surgery was performed on the whole arm type paralysis in 12 patients, lower arm type paralysis in 8 patients. The preoperative visual analog scale score was 8.7(7~10). When the trapezius and serratus anterior muscle were in function, operation was performed. 18 patients were processed to the additional operation. Gracilis free flap in 6 patients, neurotization in 3, Steindler flexor plasty in 6, and tendon transfer in 3 were performed. Fixation was conducted with cancellous screws in 13 patients, Knoles pins in 5, and cancellous screws and Knoles pins in 2. The position of the arthrodesis at operation was $28.5^{circ}$($20~45^{circ}$) in abduction, $30.3^{circ}$($20~45^{circ}$) in flexion, and $30.8^{circ}$($20~40^{circ}$) in internal rotation. Result: The follow up visual analog scale score was 3.4(0~7). Postoperatively, shoulder spica cast was applied for 15.3weeks(8-20weeks). The median time to bony union was 17.7weeks(9~28weeks). Average range of motion was $32.0^{circ}$($15~40^{circ}$) of abduction, $24.0^{circ}$($10~40^{circ}$) of flexion, and $18.5^{circ}$($10~30^{circ}$)of internal rotation. Conclusion: The shoulder fusion in brachial plexus injury patients is one of the good methods to relieve pain, improve the function and stabilize the flail shoulder joint.