The purpose of this study was to evaluate the common modes of fixation failure in unstable intertrochanteric fractures , related risk factors and the prevention of fixation failure. Between 1995 and 2001, 44 patients who had sustained an unstable intertrochanteric fractures were assigned to be treated with a sliding hip screw. Men in 14 cases ( 32% ), women in 30 cases ( 68% ) , the average age at the operation was 65(22-90) years and the average duration of follow up was 12(8-22) months. We classified the fracture patterns with Evans system and used Singh 's index for osteoporosis. And we examined the common modes of fixation failure with postoperative X-ray. The fixation failure in unstable intertrochanteric fracture was 8 cases (18.2 % ); varus collapse of the proximal fragment with cutout of the lag screw was 3 cases (6.8%), varus collapse of the proximal fragment with excessive sliding of the lag screw was 4 cases (9.1%) and loss of fixation of the plate-holding screws was 1 case (2.3%). The authors think that inadequate anatomical reduction of comminuted posteromedial fragment and severity of osteoporosis are main causes of fixation failure. During operation for unstable intertrochanteric fractures, the most important point is accurate reduction of posteromedial fragment and the intramedullary hip screw like proximal femoral nail ( PFN ) may be considered to avoid fracture of lateral cortex that enter the lag screw, causing fixation failure.