PURPOSE: The purpose of this study is to evaluate the effectiveness of operative methods for diaphyseal fractures of both forearm bones in adults. MATERIALS AND METHODS: Forty five cases with diaphyseal fractures of both forearm bones over 18 year old that are treated by operative methods from January 1994 to December 1998 were followed and analyzed. The most common age group was 3rd and 4th decade(each, 24.4%). Traffic accident was the most common cause of injuries(31.2%). Among both the radius and ulna, middle 1/3 was the most common level of fractures(60%, 57.8%). In operative methods, open redeuction and internal fixation with dynamic compression plate(D.C.P.) and screws were performed in 39 cases, closed reduction and internal fixation with Rush pin were performed in 5 cases, And another 1 case was performed with D.C.P. and Rush pin simultaneously. RESULTS: According to simple X-ray and physical examinations, The average of bone union periods was 12.7 weeks in radius, 13.5 weeks in ulna. The range of bone union periods according to the level of fractures was from 12.4 weeks to 14.1 weeks. For the functional results assessed by Grace and Eversmann method, excellent was 48.9%, good was 35.6%, acceptable was 11.1% and unacceptable was 4.4%. CONCLUSION: The functional result was satisfactory in 84.5%. So the operative method of diaphyseal fractures of both forearm bones, if proper operative method had been selected and meticulous surgical technique had been performed, was considered as recommendable method.