The authers reviewed 15 patients of open fracture of the tibial shaft who were treated by external fixation followed by intramedullary nailing. These fractures comprised two Type-I, two Type-II, four Type-IIIa, and seven Type-IIIb injuries. Ten patients were treated with unreamed intramedullary nailing and 5 patients were treated with reamed intramedullary nailing. The results were analyzed as followings: 1. All fractures had union at 5.2 months after intramedullary nailing and 4 true osteomyelitis were developed. 2. All osteomyelitis were developed for the patients who were treated with reamed intramedullary nailing. 3. There was no osteomyelitis who were treated with unreamed intramedullary nailing. 4. Delayed conversion to intramedullary nailing after control of pin tract infection had no effect for prevention of osteomyelitis.