Shoulder arthrodesis is often used to treat flail shoulder after a brachial plexus injury, but has a high complication rate and entails loss of passive mobility. We have reviewed 27 patients with brachial plexus injury treated by transfer of the trapezius to the proximal humerus at an average time from injury of 31.3 months. Pre-operatively, all 27 shoulders were subluxated, with an average abduction of 3.5 degrees. Postoperatively, shoulder abduction averaged 45.4 degrees, and subluxation was abolished. All patients were satisfied with their improvement in function. Trapezius transfer is recommended as a simple procedure that requires only a brief period in hospital, allows early rehabilitation, and gives a satisfactory outcome, while retaining passive mobility of the shoulder.