PURPOSE: To evaluate the usefulness of unreamed nailing inthe treatment of femoral shaft fractures. MATERIALS AND METHODS: Between March 1996 and June 1998, unreamed nailing with closed method was done for 74 patients with 82 femoral shaft fractures. The main indications for this treatment were multiple injury or isolated femoral fracture above Winquist type II. The influence of Winquist- Hansen classification, anatomical location, and open injury over bone union and the influence of injury severity score over general complication including fat embolism were investigated. RESULTS: Primary union occurred in 76 cases(93%) with 6 cases of nonunion and 10(12%) of delayed union, and mean time to union was 27 weeks. In open fractures, the union time was delayed(32 weeks) rather than closed fracture. In Winquist classification, there was no stastical importance on time to union, but nonunion was most common in Winquist type IV. Anatomical location has no influence on time to union. In the view point of multiple injury, the group above 18 points(31 patients) in injury severity score had none of fat embolism, but the group below 18 points(43 patients) had 2 patients. CONCLUSION: The treatment of femoral shaft fractures by unreamed nailing had longer time to union with higher rate of delayed union, and we think that the theoretical advantage of decreasing pulmonary complications is controversial.