Recently, arthroscopic surgical techniques have been reported for release of glenohumeral capsular contractures in selected patients with frozen-shoulder syndrome. The purpose of the current study was to assess the anatomy and histology of the subscapularis muscle, including its intra-articular component. Ten cadaveric shoulders underwent arthroscopy and dissection, and an additional 3 specimens underwent histological analysis. To provide clinical correlation, 35 patients who underwent arthroscopic capsular release completed a modified questionnaire developed by the authors. The anterior-posterior diameter and cephalad-caudad height of the intra-articular subscapularis tendon (IASS) averaged 5 mm and 11 mm, respectively. This represented 83% of the sagittal diameter and 25% of the total height of the subscapularis at the point of release. Histological analysis confirmed these anatomic observations. All patients had reduction of pain and improved function at an average of 22 months after surgery. Only 1 patient had mild subjective symptoms of instability. The current study indicates that the IASS can be released during arthroscopic capsular release for frozen shoulder with minimal risk of secondary anterior instability to the patient.