During a period of forty-two years, twenty patients who had a post-traumatic proximal radio-ulnar synostosis were treated by excision of the area of synostosis and various concurrent procedures in an attempt to restore rotation of the forearm. The time from injury to operation averaged eighteen months, and the postoperative follow-up averaged forty months. Results were graded on the basis of improvement in the arc of rotation of the forearm. After excision of the area of synostosis in the fifteen patients for whom data were available, the intraoperative arc of passive rotation averaged 121 degrees. At the most recent follow-up, the range of active rotation averaged 55 degrees for all twenty patients. Four patients had an excellent result; three, good; four, fair; and nine, poor. The outcome of this type of surgical treatment varies, but roughly half of the patients can be benefited.