Over a 5-year period, 75 shoulders that met Codman's criteria for primary frozen shoulder were treated. Nine patients improved with nonoperative treatment, and the remaining 66 patients underwent manipulation under anesthesia. The shoulders in 41 patients successfully released with manipulation. Those in 25 failed to release with manipulation, and therefore, these patients underwent open surgical release of the contracted shoulder. We reviewed the cases of all of the surgically treated patients at 19.52 months' average follow-up, using the history and clinical examination technique recommended by the American Shoulder and Elbow Surgeons. The surgical findings in this group of 25 patients showed a consistent alteration in the rotator interval and coracohumeral ligament. The rotator interval was obliterated, and the coracohumeral ligament was transformed into a tough contracted band. The histology of this contracture was examined in 12 patients and consisted of a dense matrix of type III collagen populated with fibroblasts and myofibroblasts. The contracted coracohumeral ligament was excised with immediate release of the external rotation deficit. Pain scores on visual analogue scale improved from 8.28 to 2.0. The average score for function, with a maximum score of 30, improved from 6.08 to 18.9. Twenty patients had excellent or good results, and 3 had fair results. The shoulders of 2 patients failed to improve: 1 was an insulin-dependent patient with diabetes, and 1 had severe bilateral Dupuytren's contractures. The results in the patients without diabetes were very satisfactory, with visual analogue scale scores of pain decreasing from 8.4 to 1.1, function increasing from 6.4 to 20.1, flexion increasing from an average of 96 degrees to an average of 131 degrees, and external rotation increasing from an average of 10.0 degrees to an average of 46.7 degrees. Surgical release of frozen shoulder is a useful option in those few patients with severe disease whose shoulders fail to release with manipulation under anesthesia. Caution should be used in insulin-dependent patients with diabetes.