The results of an operative approach to the problem of radio-ulnar synostosis were assessed in thirteen patients, ten to twenty-five and one-half years after the procedure was performed. We concluded that in a patient with bilateral synostosis one hand, the one not used in writing, should be shifted to a position of 20 to 35 degrees of supination. With one hand in this position, the other may be left in considerable pronation. Often after such a shift it is not necessary to rotate the second arm. However, if the pronation is marked in the second forearm, and if function is impaired unduly by this position, surgical correction is indicated. The arm should be placed in a position of 30 to 45 degrees of pronation. In unilateral radio-unlar synostosis, the ordinarily ideal position of the radius is between 10 and 20 degrees of supination. In an adult, the patient's occupation should be considered in deciding on the rotatory positions of the forearms. We usually prefer a method of transverse osteotomy through the conjoined mass of the radius and ulna. Careful observation of the effect on the vascular status of the limb during and immediately after surgery is important.