BACKGROUND: Persisting shoulder stiffness adversely affects quality of life by causing pain and motion restrictions especially in patients with diabetes. OBJECTIVE: The aim of this study was to evaluate the outcomes of arthroscopic capsular release in patients with idiopathic shoulder stiffness. METHOD: A literature search was conducted in electronic databases and studies were selected by following precise eligibility criteria. Random-effects meta-analyses were performed to estimate the changes at latest follow-up in scores of the Constant, American Shoulder and Elbow Surgeons (ASES), and University of California at Los Angelis (UCLA) scales, Visual Analogue Scale (VAS), and shoulder range of motion. RESULTS: Nineteen studies were included. The follow-up duration was 42 months [95% confidence interval (CI): 32, 51]. Improvements in scores of the Constant, ASES, UCLA scales, and VAS were 48.3 [95% CI: 38.0, 58.6], 44.6 [95% CI: 24.6, 64.6], 19.3 [95% CI: 16.6, 22.0], and - 6.1 [95% CI: - 6.9, - 5.4] respectively (P < 0.05 all). Improvements in the shoulder range of motion were: abduction 82.0 [95% CI: 65.0, 98.9]; forward flexion 75.9 [95% CI: 59.7, 92.1]; external rotation 43.2 [95% CI: 37.5, 49.0]; and internal rotation 25.4 [95% CI: 15.2, 35.5] degrees; P < 0.05 all). CONCLUSION: Arthroscopic capsular release effectively improves shoulder function in patients with idiopathic shoulder stiffness. [ABSTRACT FROM AUTHOR]