Management of severe diaphyseal fracture of radius and ulna in children can be a challenging problem. Reduction and maintenance of the position of two mobile parallel bones is difficult because pronating and supinating muscles produce angulatory as well as rotational forces. Open reduction and internal fixation are generally accepted for adult forearm fractures, but controversy surrounds open reduction for children. What should be done for the irreducible fracture that will result in a malunion? Several authors advocate open reduction in children over 10 years of age rather than accept poor position. And others advocate open reduction regardless of age if closed reduction is unsatisfactory. We reviewed thirteen children between 6-14 years of age, who had irreducible fractures of diaphysis of forearm both bone, and who were treated with open reduction and internal fixation with plate for mid 1/3 fractures(4 cases) and open reduction and internal fixation with K-wires for distal 1/3 fractures(9 cases). The results were as follows; 1. 2 cases(15%) had limitation of pronation within 10 comparing with uninjured side. But 11 cases(85%) had equal movements on both sides. And the range of motions of the elbow and wrist are within normal limit. 2. More than 20 angulation for mid 1/3 fracture over 10 years of age, and more than 20 angulation or 20% displacement for distal 1/3 fracture over 6 years of age, it would be better to perform a surgical treatment if nonsurgical treatment was failed. 3. Immobilization periods were 5 weeks for plate fixation group and 6.9 weeks for K-wire fixatioin group. Bone union was occurred in all cases, at 9 weeks in plate fixation group and 8 weeks in K-wire fixation group. 4. Its better to fix with plate ofr promimal 2/3 fracture and K-wire for distal 1/3 fracture in case of operation. In conclusion, our results of open reduction and internal fixation were satisfactory if adequate alignment of fractures had not been achieved or maintained.