We present the results of a new mobilization procedure for the treatment of a congenital proximal radioulnar synostosis in seven patients. The operative procedure included separation of the synostosis and placement of a free vascularized fascio-fat graft to prevent recurrent ankylosis. The average age at the time of the operation was eight years and two months (range, six years and four months to eleven years and ten months). All of the patients were boys who had no other congenital anomalies. The radial head was dislocated in all seven patients (anteriorly in two and posteriorly in five). The final four index operations included an osteotomy of the radius in order to reduce the dislocated radial head. The average duration of follow-up was three years and eight months (range, two years and four months to four years and five months).Preoperatively, the patients had had difficulty with holding a bowl of soup and accepting objects, such as coins, into the palm. Postoperatively, they were able to perform these activities. None of the patients had recurrent ankylosis or loss of the flap. The average supination was 26 degrees (range, 10 to 45 degrees), and the average pronation was 45 degrees (range, 10 to 80 degrees). The four patients who had had an osteotomy of the radius in addition to the index procedure did not have a dislocation of the radial head and had an average arc of motion of 83 degrees of pronation and supination. The three patients who had not had an osteotomy had a dislocation of the radial head and an average arc of motion of 40 degrees after the index procedure.These findings demonstrate that separation of a congenital radioulnar synostosis with a vascularized fascio-fat graft and osteotomy of the radius can achieve pronation and supination of the forearm.