Purpose: The objective of this study is to evaluate the functional outcome and identify prognosis of retear patients in patients aged 65 years or over undergoing surgical repair for a large to massive full-thickness rotator cuff tear. Materials and Methods: From 1995 September to 2010 March, 147 patients aged 65years or over (40 male, 107 female, with an average age of 69.6) undergoing surgical repair for large to massive full thickness rotator cuff tear (large 67 cases, massive 80 cases). For functional evaluation, preoperative and postoperative 1 year range of motion and muscle power checked. For subjective evaluation, American shoulder and elbow surgeons score and Constant score were checked. For anatomical evaluation, 87 patients were checked shoulder MRI at the time of the postoperative 1 year. Results: ASES score improved from to 50.4 to 88.9, Constant score improved from 47.1 to 75.2. Supraspinatus power improved from 51.1% to 80.8%, external rotator muscle power improved from 64.5% to 83.1%. Forward elevation improved from 117.4 degrees to 153 degrees, external rotation improved from 23.6 degrees to 41.8 degrees. Follow up MRI showed re-tear in 23%, all re-tear patients were from massive tear except one patient. All re-tear patients showed improved clinical outcomes, but supraspinatus and external rotator muscle power were not improved. Conclusions: Patients aged 65 years or over undergoing surgical repair for a large to massive full-thickness rotator cuff tear showed successful outcomes over 90 percent. Re-tear patients also showed successful clinical outcomes. In elderly patients with large to massive full thickness rotator cuff tear, aggressive surgical repair leads good clinical outcomes.