PURPOSE: To evaluate causes, treatment methods, outcomes and usefulness of external fixator after we have treated patients with proximal tibial nonunion successfully using external fixator. MATERIALS AND METHODS: We treated the 10 patients with proximal tibial nonunion between December, 1991 and December, 2000. Mean follow-up period was 18.5 months. We analyzed numbers of operations, operative methods and causes of nonunion, and rated bony and functional results according to Paley's classification. RESULTS: The causes of nonunion were infection in 6 cases, insecure fixation in 4 cases. Bony union was achieved in all 10 cases. The mean time of union was 12.9 months. Complications were developed in 8 cases. Pin site infection occurred in 7 cases, pain in 8 cases, joint stiffness in 2 cases, angular deformity in 2 cases. Functional results were excellent in one, good in four, fair in three, poor in two. CONCLUSIONS: We concluded that external fixation method using external fixator such as Ilizarov in treating nonunion of proximal tibia was very useful because of offering advantages of bony shortening and compression, bony lengthening, bone grafting and early weight bearing in patient with infected nonunion and bone defect with many complications