A review of 385 proximal fractures of the femur treated with a telescopic screw system revealed that in nine cases the device had cut out of the head of the femur necessitating its removal. In two cases the head of the femur had been penetrated at the time of insertion. In all but one of the remaining seven cases the screw had been inserted in the superior half of the head and neck of the femur. The overall cut-out rate was 2.25 per cent but was 11.9 per cent when the screw was placed in the superior half of the head. When the screw was placed in the inferior half of the head, the cut-out rate was only 0.29 per cent. There was no correlation between this mechanical failure and age, sex, type of fracture or the presence of metabolic bone disease. These results indicate that if this otherwise effective form of internal fixation is to be used in the treatment of proximal fractures of the femur, care must be taken to avoid placement of the device in the superior half of the head and neck of the femur.