Although much has been published regarding shoulder manipulation under anesthesia for the treatment of frozen shoulder, there are no reported long-term results. In 25 patients (26 shoulders) in whom nonoperative treatment for idiopathic frozen shoulder had failed, we performed manipulation under anesthesia. All had had physical therapy for a mean of 6.2 months. Follow-up was by examination until the end of active treatment. Longer-term follow-up was obtained in 18 patients (19 shoulders) by questionnaire and averaged 15 years (range, 8.1 to 20.6 years). There were significant improvements in forward elevation from a mean of 104 degrees before manipulation (range, 70 degrees to 140 degrees ) to 168 degrees (range, 90 degrees to 180 degrees ) and in external rotation from 23 degrees (range, -5 degrees to 70 degrees ) to 67 degrees (range, 0 degrees to 90 degrees ). There were 16 shoulders with no pain or slight pain and 3 with occasional moderate or severe pain. There were no fractures, dislocations, or other complications. Of the 19 shoulders, 18 required no further surgery. At long-term follow-up, the mean Simple Shoulder Test score was 9.5 out of 12 and the mean American Shoulder and Elbow Surgeons score was 80 out of 100. Treatment of idiopathic frozen shoulder by manipulation under anesthesia leads to sustained improvement in shoulder motion and function at a mean of 15 years after the procedure.