PURPOSE: The malunited diaphyseal tibia fractures result in tibial shortening, angular deformities, gait disturbance, development of joint pain, etc. The authors analyzed the results of treatment consist of corrective osteotomy for diaphyseal malunion with internal or external fixation. MATERIALS AND METHODS: The authors reviewed 18 cases of tibial diaphyseal malunion treated in Korea Veterans Hospital between January 1992 and December 1998. Mean follow-up period was 4.2 years. The preoperative deformities were varus, anterior or posterior bowing and shortening. The preoperative symptoms were knee joint pain, ankle joint pain, and gait disturbance. Corrective osteotomy was done on the site of malunion in all cases. Fixation were done with IM nailings(13 cases), plates(3 cases) and Ilizarov external fixator. We analyzed the unions radiologically and the knee pains with HSS score. RESULTS: All malunions were successfully corrected. Mean duration of union was 4.5 month. In the coronal plane, preoperative varus deformity(mean 16.5degrees varus) was corrected to 3degrees of valgus. In the saggital plane, anterior and posterior bowing was corrected to neutral. In 15 cases of the patient with knee joint pain, the mean HSS score was improved from 69 preopertively to 82 postoperatively. CONCLUSION: The correction of tibia diaphyseal malunion had good results by osteotomy at the malunited site and firm internal or external fixation. And it also improved knee joint pain significantly.