PURPOSE: The aims of this study were to investigate the prevalence and the causes of screw breakage in tibia nailing. MATERIALS AND METHODS: Between 1995 and 2000, eighty-two tibial diaphyseal fractures were treated with interlocking nails. The loss of follow-up was 7 cases. We retrospectively reviewed seventy-five cases. We investigated the rate and location of metal failure and evaluated the fracture pattern, the presence of distraction after nailing and union abnormality. RESULTS: Screw breakage was identified in seven cases (9.3%) and most frequently occurred on the second proximal locking screw. Screw breakage occurred in AO type B or C type fractures, fracture site distraction after nailing, open fracture, delayed union and nonunion. CONCLUSION: The main cause of screw breakage is unstable bone to bone contact on the fracture site caused by comminution or distraction. The open fracture, delayed union, and nonunion also contributing factors for screw breakage. For preventing screw breakage, it is necessary to avoid fracture site distraction and delay full weight bearing in cases having unstable fracture site contact.