BACKGROUND: The purpose of the study was to compare the degree of degeneration of the articular and bursal layers of delaminated supraspinatus tendons based on histological examination. METHODS: Fifty-four patients with a full-thickness rotator cuff tear were included in the study. Tendon specimens were harvested during arthroscopic rotator cuff repair from the lateral torn edges of the articular and bursal layers of the delaminated tear. Harvested samples were stained with H&E dye and evaluated based on a semi-quantitative grading scale. RESULTS: There were no significant differences in the seven histological characteristics of tendon degeneration: fiber structure, fiber arrangement, round nuclei, regional variations in cellularity, vascularity, collagen stainability, and hyalinization between the articular and bursal layers of the delaminated rotator cuff tear (all p>0.05). Total degeneration scores of articular and bursal sides were 13.1 ± 3.85 points and 13.2 ± 3.42 points, respectively, and were not significantly different (p=0.958). CONCLUSIONS: The study demonstrates that tendon degeneration was similar in the articular and bursal sides of the delaminated fullthickness rotator cuff tear, suggesting that degeneration would be a main etiology for the rotator cuff tear not only in the articular side but also in the bursal side. Considering potential disadvantages of subacromial decompression, this study tentatively suggests routine use of subacromial decompression as well as the need for halting or recovery from rotator cuff degeneration for better rotator cuff repair.