Introduction. Latissimus dorsi transfer is a procedure used in massive irreparable posterosuperior rotator cuff tears, in young patient with severe pain and significant functional impairment. The purpose of this retrospective study was to evaluate its clinical, radiological and electromyographic results. Methods. Forteen massive irreparable posterosuperior rotator cuff tears were performed with latissimus dorsi transfer between 2000 and 2008, and were reviewed at an average follow-up of 56 months and minimum of 19 months. Five transfers were primary reconstructions, and nine were revision surgeries. Patients’ mean age was 52.7 years. Clinical outcomes were measured by the Constant score, pain level, active range of motion, and strength. Osteoarthritis and acromiohumeral distance were measured on standardized radiographs. Ultrasound examination evaluate the integrity of the tendon. Axial images in CT-scan looked for muscle atrophy of latissimus dorsi in comparison with the controlateral. Electromyographic activity was measured during active flexion, abduction, adduction and rotations. Results. Twelve patients were satisfied. At the last follow-up, the average pain level according to a 100 mm visual analog scale was 31. The mean age and gender-matched Constant and Murley score improved from 34 to 60 % (p=0.003), forward elevation from 89° to 132° (p=0.006), abduction from 92° to 104°, external rotation from 12° to 24° (p=0.015). Mean abduction and external rotation strength were measured at 2.5 kg. Osteoarthritis progressed, and mean acromio-humeral distance has a significant decrease from 7.5 mm to 4.4 mm (p=0.003). Ultrasound examination showed twelve transferred tendons healed to the greater tuberosity. CT-scan showed a small atrophy of the transferred muscle, with a measurement of the cross-sectional area of the muscle belly at the inferior angle of the scapula at 1405 mm2, versus 1644 mm2 for the controlateral (p=0.06). Electromyographic analysis demonstrated a significant higher electric activity on the operative side during abduction and external rotation, and significant lower activity during adduction and internal rotation in comparison with the nonoperative side. Conclusions. Latissimus dorsi transfer allows for significant pain relief and function improvement in irreparable posterosuperior rotator cuff tears at young patients. Its electric activity increase in abduction and external rotation shows that the transferred muscle can integrate a new function and act like an active muscle transfer, in addition to an interposition or tenodesis effect. However we didn't find any depression of the humeral head or strength improvement