BACKGROUND: Assessment of the clinical outcomes after rotator cuff repair is essential for their effectiveness on treatment. The Korean Shoulder and Elbow Society devised the Korean Shoulder Scoring System (KSS) for patients with rotator cuff disorder. The purpose of this study was to evaluate the availability of the KSS for assessment of clinical outcomes in patients after arthroscopic rotator cuff repair, and for comparison with other appraisal scoring systems. METHODS: A total of 130 patients with partial-thickness or full-thickness rotator cuff tear who underwent arthroscopic repair using a single row or double row suture bridge technique were enrolled. The average follow-up period was 25.9 months. All patients were classified according to various factors. Comparison within corresponding categories was performed, and the correlation between the KSS and other shoulder assessment methods including University of California Los Angeles (UCLA), Constant and American Shoulder and Elbow Surgeons (ASES) score was analyzed. RESULTS: Total score of the KSS response had increased from 59.6 preoperatively to 88.96 at last follow-up. All KSS domains, including function, pain, satisfaction, range of motion, and muscle power had improved up to 24 months postoperatively. Statistical significance was observed mainly in preoperative measurements with number and size of torn tendons, and greater than or equal to grade 3 of fatty infiltration. The KSS was best correlated with the UCLA scoring system in both preoperative (r=0.785) and postoperative (r=0.951) measurements. CONCLUSIONS: The KSS was highly reliable and valid as a discriminative instrument, and it showed strong correlation with ASES and UCLA scoring systems.