To compare the clinical and radiologic outcomes of chronically retracted rotator cuff tears by arthroscopic medializing and non-medializing repair (restoring anatomic footprint and performing conventional repair). This study retrospectively reviewed 195 patients who underwent arthroscopic double-row modified Mason-Allen repair for large, full-thickness rotator cuff tears from January 2013 to July 2015. We included a total of 60 of these patients and divided them into 2 groups: those who underwent medialization (n= 24) and those who did not (n= 36). Magnetic resonance imaging was performed at a minimum of 6months (mean, 15.2months; range, 6-24months) postoperatively to assess cuff integrity. Patients were clinically evaluated at least 1year postoperatively (mean, 18.9months; range, 12-60months) with a visual analog scale, the American Shoulder and Elbow Surgeons score, the University of California-Los Angeles Shoulder Rating Scale score, and the Constant score. The mean medialization length was 10.5mm (range, 6.5-15.6mm) on magnetic resonance imaging. The retear rate was 8.3% (n= 2) in the medialization group and 31% (n= 11) in the non-medialization group (P= .041). At last follow-up, the mean visual analog scale, American Shoulder and Elbow Surgeons, University of California-Los Angeles, and Constant scores improved significantly from 5.3 ± 1.4, 38.5 ± 8.8, 22.5 ± 3.1, and 41.7 ± 9.9, respectively, to 1.8 ± 1.1, 85.3 ± 7.5, 31.8 ± 2.5, and 90.2 ± 6.9, respectively, with medialization and from 4.0 ± 1.6, 51.5 ± 10.5, 20.0 ± 3.9, and 55.9 ± 10.5, respectively, to 1.4 ± 1.0, 88.6 ± 9.0, 31.0 ± 9.3, and 89.4 ± 9.3, respectively, with non-medialization (P < .001), although there were no significant differences between the groups (P= .165, P= .653, P= .250, and P= .113, respectively). Medialization of approximately 10.5mm reliably shows good clinical results, and medializing rotator cuff tendons should be considered as a treatment option for repairing rotator cuff tears with chronic retracted tendons. Level III, retrospective comparative study.