In the treatment of tibial shaft fracture with intramedullary nail, reaming effectively lengthens the isthmus of the tibia and there by extends the number of fractures amenable to this technique. Reming process, however, destroys the endosteal blood supply, may impair bony union and provocate infection in open fracture. Eighty-eight cases of tibial shaft fractures treated with reamed nail(56 cases) and unreamed nail(32 cases) from January l991 to August 1994 at Yonsei Medical Center were analyzed. Average follow-up period was 7.3 months. Results were as follows; 1. In closed fractures, there was no difference in union time between reamed and unreamed group, and low energy injury group had shorter union time than high energy injury group. 2. In open fractures, unreamed group had shorter union time than reamed group. 3. Unreamed group had less complications such as infection and delayed union, and had more cases of interlocking screw breakage(3 cases) which did not dusturb the bony union. In conclusion, unreamed tibial nailing was useful method to treat not only open fracture but also closed fracture.