Congenital radioulnar synostosis can be a disabling state, especially if it is bilateral or fixed hyperpronation. The purpose of this study is to introduce the surgical technique in proximal radioulnar synostosis who needs surgical intervention. Our procedures included excision of synostosis, interposition of muscle flap using brachioradialis, anconeus or extensor carpi ulnaris muscles with vascular pedicle for prevention of re-ankylosis and biceps transfer to improve supination. From July 1994 to July 1996, we evaluated 8 cases in 6 patients who underwent these procedures. The average age was 7 years and average duration of follow up was 24 months. The fixed forearms with hyperpronation have gained average 40 degrees of range of rotation. Improvement in holding and using small objects, sports activities and daily living activities was observed in all cases. There were no significant complications including re-ankylosis during the follow-up periods. In conclusion, surgical treatment of congenital radioulnar synostosis with these procedures is a reliable method that prevent re-ankylosis with providing forearm rotation.