The authors report a series of 38 patients who had been examined by MRI and then operated for a rotator cuff syndrome. The correlation between the description of the cuff lesions after MRI and the surgical observations were excellent for 37 patients. In one case MRI showed a false image of tear of the supra spinatus m. on its anterior edge. This was due to a bad knowledge of the anatomy of the muscle and tendon and to a poor orientation of the frontal cut plane. This study was completed with MRI and anatomic study of 12 non embalmed cadaveric shoulders. The results showed that MRI was very sensitive (0.93) and specific (0.94) for the diagnosis of rotator cuff tears. MRI allowed also to show partial tears of the tendons of the rotator cuff. The authors propose a MRI classification of cuff lesions which permits to establish a good surgical planning.