There are many difficult problems and various methods in the treatment of difficult fractures of the femur. We reviewed the records of twelve patients who had been managed with circular external fixation using the llizarov apparatus for difficult fractures of the femur at Keimyung University. Dongsan rnedical center from October 1993 to April l996. There were ten males and two females with an average age of 42 years (range, 16-74 years). Si.x of twelve patients were severely comminuted supracondylar and intercondylar fractures of the femur associated with severe soft tissue injury (including four open fractures). These patients were treated initially by closed reduction with Ilizarov external fixator and followed by compression-distraction techniques. Four of the remaining six ptients developed infected non-unions after internal fixation of the femur without shortening or bone defect. These infected non-unions were treated by curettage, irrigation and Ilizarov application. After the control of infection, compression - distraction techniques were applied. One of the remaining two patients had severe open comminuted fracture of the supra-intercondyle region of femur associated with diaphyseal segmental bone defect (5cm in length). This patient was treated with closed reduction and internal bone transportation usipg llizarov external fixator. One patient with varus deformity (20 degree) was treated by correction of the deformity and simple compression technique. In three patients, additional autogenous cancellous iliac bone graft was done. The union of the fracture site was obtained in ten patients and the duration of llizarov external fixation was an average of 10 months (range 6-14 months). We experienced several complications; there were twelve patients of limitation of motion of knee, ten patients of pin tract infection, one patient of fracture site non-union, one patient of re-fracture and one patient of femoral artery injury. We concluded that the Ilizarov external fixation technique is one of the effective methods for the treatment of difficult fractures of the femur in spite of its complexity and high incidence of complications.