Operative internal fixation of femoral fractures is widely accepted as the best method of treatment but the techniques are by no means devoid of complications, nor are they simple to execute. A method of treatment must be based on the analysis of the :"personality of the fracture", that is, the nature of the fracture and of patient. Mechanical failure such as metal failure, loosening of screw or nail after internal fixation, residual deformity, and nonunion, may impose serious problems on the surgeon and patient unless treatment is appropriate. The authors analyzed 14 mechanical failures of internal fixation in 12 femoral fractures from Dec. 1987 to Aug. 1992 in the department of orthopedic surgery, Ansan Hospital Korea University to study the possible cause of mechanical failure of internal fixation and pursue the way of reducing that complications and obtained the following results. 1. Eleven were males and one was female, most of them were in age of active life. 2. The level of fractures in 12 femorals were subtrochanteric in two, shaft in nine and supracondylar in one. 3. The time interval between internal fixation and failure in 10 failures was 5.5 months on average(range, 3month to 11months). It was uncertain in 4 failures. 4. Mechanical failure were presented as breakage in five plates, loosening of screw in five plates, loosening of screw in two DCP fixation, loosening of nail in one interlocking nail, bending of nail in one Kuntscher nail, one breakage and one bending in two condylar buttres plates, and cutting-out of hip screw in three compression hip screw. 5. The causes of failure were presumed to be improper surgical technique in 7 failures, inadequate selection of internal fixatives in 5 failures, and inadequate postoperative care in 1 case.