The case notes and radiographs of 108 patients who had undergone compression screw fixation of trochanteric fractures of the femur were reviewed. Forty-seven patients had unstable comminuted fractures, and 20 of these had medial displacement osteotomies performed. In 40% of this group the operation was not a success in terms of extrusion of the screw through the femoral head, compared with 20% for the whole series of 108 patients. A number of parameters were studied in the search for a cause for the failure, and there was a correlation with a superior position of the screw initially, and a low serum albumin. Although the proximal fragment abutted the plate at the time of operation, the medial cortices of the proximal and distal fragments were often not in apposition, allowing the fracture to collapse into varus with resultant extrusion. Unless a stable configuration is achieved at the time of operation, reliance on the sliding component of these implants to allow for collapse at the fracture site will not necessarily produce this stability, and failure will ensue.