Background: The purpose of this study was to investigate the role of coracoacromial ligament degeneration and specific anatomic parameters in the etiology of partial-thickness rotator cuff tears. Materials and Methods: This study retrospectively assessed 96 patients (mean age, 50.1 years [17-76]; 34 men, 62 women) diagnosed with bursal-side and articular-side rotator cuff tears with a history of failed conservative treatment and persistent shoulder pain who underwent arthroscopic surgery. Video records of the surgery were used to evaluate the type of cuff tear, grade of coracoacromial ligament degeneration, and associated pathologic changes; preoperative magnetic resonance images were used to measure acromioglenoid angle, supraspinatus glenoid angle, and subacromial distance. Results: Most of the patients with articular-side tears demonstrated grade 0 and grade 1 coracoacromial ligament degeneration, whereas patients with bursal-side tears had grade 1 and grade 2. There was a significant positive correlation between the grade of coracoacromial ligament degeneration and bursal-side partial rotator cuff tears, whereas no correlation was observed with articular-side tears. There was no significant difference between bursal-side and articular-side partial cuff tears regarding acromioglenoid angle, supraspinatus glenoid angle, and subacromial distance. Conclusions: Grade 1 and grade 2 coracoacromial ligament degeneration is a strong predictive factor for impingement syndrome in the etiology of bursal-side partial cuff tears and can guide the surgeon to consider ligament release and debridement or acromioplasty in these patients. (C) 2016 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.