Cut-out of the lag screw is the commonest cause of fixation failure after sliding hip screw fixation of extracapsular hip fracture. A number of technical aspects of surgery have been used to asses the risk of cut-out. This study was to determine which of these indicators was the most reliable predictor of cut-out. The anterior-posterior and lateral post-operative radiographs of 23 cases of cut-out were compared with those of 77 cases of uneventful fracture healing. The tip-apex distance with correction for magnification was found to show the most significant difference between patients with cut-out against those without (P = 0.001), followed by the lag screw position on the lateral radiographs (P = 0.0095 and 0.014), reduction of the fracture on the anterior-posterior radiograph (P = 0.011 and 0.016) and the uncorrected tip-apex distance (P = 0.019). We recommend that for audit and research purposes the corrected tip-apex distance, fracture reduction and implant positioning methods should be used. For routine clinical practice, the uncorrected tip to apex distance, which is sum of the distance from the tip of the lag screw to the apex of the femoral head on anterior-posterior and lateral radiograph, and fracture reduction angle on the anterior-posterior radiograph are recommended.