A preoperative computed tomography (CT) scan grading muscular fatty degeneration in five stages was done in 63 patients scheduled for repair of a torn rotator cuff. The results were compared with postoperative evaluation done after a mean of 17.7 months in 57 patients. Postoperative arthrographies were also performed in 56 patients. Preoperative CT scans demonstrated that infraspinatus fatty degeneration can occur in the presence of large anterosuperior tears even when the infraspinatus tendon is not torn; it worsens with time. The subscapularis rarely degenerates, and when it does it degenerates moderately, even when its tendon is not torn. After an effective surgical repair, moderate supraspinatus degeneration regressed in six of 14 patients; that of the infraspinatus never regressed but rather, increased, in three patients. One of these deteriorations, involving both supra- and infraspinatus, could probably be attributed to a partial subscapular nerve injury. Infraspinatus degeneration was correlated with functional pre- and postoperative impairment of active external rotation. Recurrence of infraspinatus tear was never observed, but recurrence occurred in 25% of supraspinatus repairs. Infraspinatus degeneration had a highly negative influence on the outcome of supraspinatus repairs. It seems preferable to operate on wide tears before irreversible muscular damage takes place.