Nonunion or delayed union of the tibia is a relatively common problem. Interlocking nailing with reaming offers the advantage of stable fixation, adequate alignment, minimum shortening, good rotational control, early weight bearing without external support and high union rate. So we treated the 25 patients of the delayed or nonunion of the tibia by interlocking nailing with reaming between July, 1986 and June, 1991. The results were as follows; 1. 25 cases consisted of 9 delayed union and 16 nonunion. Previous methods of treatment were plate and screw fixation 7, Kuntscher nailing 2 and conservative treatment 2 in 11 cases of closed fracture. 2 of type I, 12 of type II and III were treated with Ender nailing or external fixation in 14 cases of open fracture. 2. Of the 25 cases, 13 were treated with the closed nailing and 12 open nailing. 8 cases were performed the iliac bone graft and 4 fibular osteotomy. 3. Radiologically bridging callus was appeared at the average 3.8 months and complete union was obtained at average 7.6 months. 4. Of the 25 patients, 1 had postoperative deep infection; 1, proximal screw breakage; 2, proximal protrusion of nail; and 2 pain near the entry of nail. But all patients were obtained the complete union. I thought that interlocking nailing was useful to treat delayed or nonunion of the tibia fractures if there was no active infection or large soft tissue defect.