Background: Partial-thickness rotator cuff tears are a common cause of shoulder pain, yet the appropriate surgical treatment is controversial. In particular, very little information is available regarding rotator cuff integrity after operative repair. The purpose of this study was to evaluate the functional outcome and anatomic healing rate after arthroscopic repair of high-grade partial (>50%) thickness tears of the supraspinatus tendon. Methods: Forty-one consecutive patients (forty-two shoulders) who had undergone arthroscopic conversion of a partial-thickness rotator cuff tear to a full-thickness tear and subsequent repair were evaluated with ultrasound for evidence of rotator cuff healing. Clinical outcomes were assessed with use of validated outcomes measures, and all patients were reexamined by an independent observer. Results: The average patient age was fifty-three years. Thirty-seven (88%) of the forty-two shoulders had an intact rotator cuff repair seen on ultrasound at an average of eleven months postoperatively. The remaining five patients had a full-thickness defect in the tendon. The mean American Shoulder and Elbow Surgeons (ASES) score improved from 46.1 points preoperatively to 82.1 points at the time of follow-up. The overall rate of patient satisfaction was 93%. The average age of the patients with an intact rotator cuff was 51.8 years compared with 62.6 years for those with a persistent defect (p = 0.02). Conclusions: Arthroscopic repair of high-grade partial-thickness rotator cuff tears results in a high rate of tendon healing. Patient age is an important factor in tendon healing. Level of Evidence: Therapeutic Level IV. See Instructions to Authors for a complete description of levels of evidence.