Interlocking and Ender nail fixations have been widely used for the surgical treatment of diaphyseal fractures of femur. Interlocking nail could give advantage of high stability to unstable, cominuted fractures. It requires, however, advanced technique and exposure to radiation harzard, often complicated by further comminution, displacement, breakage of drill bit or loosening of locking screws. Ender nail, on the contrary, is easier in procedure without reaming, thereby maintaining endosteum and requiring short operation time. It, however, cannot avoid complications of shortening, rotational deformity, migration of nails, etc. This study aimed at comparative evaluation of the clinical results of two different nailings(23 Interlocking and 19 Ender nails) performed from March 1987 to March 1993. The study materials were 42 femoral fractures out of 41 adult patients with the followed-up between one and seven years(average 3.5 years). The results are summarized as below: 1. Fracture occurred mostly in the mid-diaphysis(81%) and the Type III comminution(63%) was most common according to the Winquist-Hansen classifiaction. 2. The operative time averaged ninty five minutes in Interlocking nailing, while sixty minutes in Ender nailing. The blood loss was negligible in both techniques. 3. Fluoroscopic assessment after insertion of the nails revealed that Interlocking gave superior stability to Ender nail, while Ender nail produced earlier callus formation(7.5 weeks in average) than Interlocking nail(9.0 weeks in average, p<0.05). It took both nails average eighteen weeks to obtain clinical union(p>0.05). 4. Interlocking nail was complicated by loosening of locking screws in two, angulation in one, breakage of drill bit in one cases. Ender nail showed protrusion in two, limb shortening in three, rotational deformity in three cases respectively. There was neither operative infection nor nonunion.