Introduction Rotator cuff tears cause severe functional impairment and pain as a result of loss of superior stability of the humeral head. Here, we focused on the treatment of defects in the superior capsule for the stabilization of irreparable tears in the rotator cuff tendon. Our previous biomechanical study in cadaveric shoulders showed that superior capsular reconstruction completely restored the superior stability of a simulated irreparable rotator cuff tear. The objective of this study was to investigate the functional and radiological results of this arthroscopic superior capsular reconstruction in the living body. Methods From 2007 to 2009, twenty-two consecutive patients (12 male and 10 female) (mean age of 65 years; range, 52 to 77 years) with irreparable supraspinatus and infraspinatus tears (9 large and 13 massive) were prospectively enrolled in the study. Mean duration of symptoms before surgery was 20 months (range, 3 to 96 months). The average follow-up was 33 months (range, 24 to 40 months). All patients underwent arthroscopic superior capsular reconstruction using fascia lata. The average dimensions of the grafted fascia lata were 3.2 × 5.9 cm. Suture anchors were used to attach the graft medially to the superior tubercle of the glenoid and laterally to the greater tuberosity. The torn subscapularis tendon in 9 patients was repaired arthroscopically. Finally, side-to-side sutures were added between the graft and the infraspinatus tendon and between the graft and the subscapularis tendon to improve force coupling in the shoulder joint. Physical examination was performed and shoulder radiographs and magnetic resonance images taken before surgery and 3, 6, 12, and 24 months after surgery. Functional outcome was evaluated by using the University of California, Los Angeles (UCLA) score. Results Mean active flexion significantly increased from 66° to 163° (P Conclusion In patients with irreparable rotator cuff tears, including subscapularis tendon tears, our arthroscopic superior capsular reconstruction restored superior stability of the humeral head, resulting in substantial improvements in shoulder function, strength, and pain relief without complications, including graft tears.