The purpose of this study was to document the diagnosis, surgical treatment, and functional outcome in patients with subscapularis ruptures after shoulder arthroplasty. Prospective objective and subjective data were collected on 7 patients with symptomatic rupture of the subscapularis tendon after shoulder arthroplasty. Presenting signs and symptoms included pain, weakness in internal rotation, increased external rotation, and anterior instability. All patients were treated with surgical repair of the ruptured tendon. Four required repair augmentation with a transfer of the pectoralis major tendon. After subscapularis repair and pectoralis transfer, 2 patients continued to have anterior instability and required an additional operation to address the instability. At a mean follow-up of 2.3 years (range, 18-55 months), the mean American Shoulder and Elbow Surgeons shoulder score in this study group was 63.2. The mean patient satisfaction rating, on a 10-point scale, was 6.2. Factors associated with post-arthroplasty subscapularis ruptures included subscapularis lengthening techniques used to address internal rotation contracture and previous surgery that violated the subscapularis tendon. Symptomatic subscapularis rupture after shoulder arthroplasty introduces the need for additional surgery and a period of protected or delayed rehabilitation after arthroplasty. Although symptoms were adequately addressed with appropriate surgical treatment, decreased functional outcomes were observed.