Congenital radioulnar synostosis can be severely disabling, especially if it is bilateral or if severe hyperpronation exists. Functionally, patients with severe deformity have trouble getting a cup to the mouth, using eating utensils, or accepting objects in an open palm. Of 33 patients (17 bilateral and 7 unilateral) underwent derotational osteotomy, with the majority being performed through the synostosis held with, an intramedullary wire and secondary transfixing device. There were eight complications, four involving neurovascular compromise. In bilateral cases, the best end position appears to be 10% to 15% of pronation in the dominant extremity and neutral in the other. Eighty-two percent of the patients had good or excellent results.