Nonunion is one of the most common complications of fracture and surgical treatment is required for union in most cases. Many kinds of treatment modalities for nonunion have been studied, but above all, rigid fixation of fractured fragments and bone graft have been the most commonly used method. In addition, development of fixation devices and electrical stimulation have contributed to solve the difficult problem on treatment of nonunion. 58 cases of nonunion were examined and treated at the Department of Orthopedic Surgery, Seoul National University Hospital from May 1985 to April 1989 and the results were as follows: 1. The frequently involved sites of nonunion were femur (38%), tibia (24%) and humerus (19 %) in order and the male patients were predominant over the females. 2. Causes of nonunion were the failure of immobilization in 25 cases (43%), soft tissue interposition in 12 cases (20%), and infecion in 11 cases (19%) in order. In the closed fracture nonunion occurred more in patients treated with the operative method, 32 cases (53,6%) than in patients treated with the nonoperative method, 15 cases (36.6%). 3. In all cases that osteosynthesis was attempted, rigid fixation and bone graft were performed with the union rate of 88.7% and the average duration for union of 6.1 months.