In most cases the genesis of brachial plexus palsy is traumatic, often because of bike accidents. If physiotherapy and neurosurgical procedures such as nerve repair do not have the desired outcome, muscle transfer operations are possible. The results of our favored transfer of the trapezius muscle to compensate paralysis of the deltoid muscle will be presented. Preoperatively radiological, clinical and electromyographic examinations are necessary. Our results are based upon the clinical and radiological check ups and the subjective assessment of the patients. Thirty-one patients (7 female, 24 male) underwent a trapezius transfer between March 1994 and December 1996. The average age was 29 years (range 18–46 years). We performed the operations using a modification of Saha's technique. With the patient in lateral decubitus position and protection of the opposite plexus, a sagital skin incision is the first step, followed by the preparation of trapezius and deltoid muscle as well as the bony parts of the shoulder (acromion, clavicle, scapular spine). The deltoid origin is cut from the lateral third of the clavicle, the acromion and the lateral half of the scapular spine. The next step is transection of the root of the acromion and the lateral clavicle. After elevation of the remaining trapezius insertions from the clavicle and scapular spine, the proximal humerus is exposured by splitting the partly detached deltoid muscle longitudinally. Then the acromion fragment and humerus are prepared for the bone-to-bone contact. In 90 ° of abduction the acromion fragment with its trapezius insertion is transferred and fixed to the humerus with two 4.5-mm screws. Finally the deltoid is sutured on the top of the trapezius and the skin is closed over two suction drains. Postoperatively we immobilize the operated arm in an abduction support for 6 weeks. The physiotherapy program starts on the first postoperative day with active training of elbow, hand and fingers and electrostimulation of the transferred trapezius muscle. Six weeks after the procedure we take an X-ray and start with progressive adduction of the arm. The preoperative subluxation of the humeral head was abolished in all cases. We achieved an average increase of active abduction from 7.3 ° (range 0–45 °) preoperatively to 39.2 ° (range 25 °–80 °) 1 year after the operation; the increase of forward flexion was from 20 ° (range 0 °–85 °) to 43 ° (range 20 °–90 °). All patients were satisfied with the improvement of stability and function of the operated shoulder. Finally we can conclude that the trapezius transfer for flail shoulder gives a satisfactory outcome regarding shoulder function and stability as well as the subjective situation of the patients.