Of the several nonoperative and operative options described for the treatment of delayed union and nonunion of the long bone, interlocking nailing with reaming offect of internal splint, autogenous bone graft and early return to a normal way of life. The purpose of this study is to evaluate the usefulness and complication of intramedullary(IM) naling with reaming by retrospective method. We treated 34 patients with delayed union or nonunion of the tibia, femur, and humerus by interlocking nailing with reaming between January 1992 and December 1996. The results were as follows ; 1. Of the 34 cases, there were 13 tibia fracture, 17 femur fracture, 4 humerus fracture. Half of them were ununited and another half were delayed in fracture healing. 2. Previous methods of treatment were conservative treatment in 2 cases, external fixator in 2, plate & screws fixation in 8, Ender nail in 2, Kuntscher nail in 2 and interlocking nail in 7 among 24 cases of cloed fracture and external fixator in 8 and interlocking nail in 2 among 10 cases of open fracture. 3. Twenty-five patients were treated with closed nailing and 9 were treated with open nailing. Iliac bone graft was performed at 3 cases and fibulotomy was performed at 1 case. 4. Union was obtained in 33 cases and 1 case needed additional bone grafting to achieve union. 5. Postoperative complications were one nonunion, two evtry site pain, one screw breakage, one heterotopic ossification, and one postoperative infection. Interlocking nailing with reaming was associated with a high union rate(97%) in our eries. The authors believe that IM nailing with reaming is a useful option for treatment of delayed or nonunion of the long bone fracture.