An unstable intertrochanteric fracture of the hip is a fracture that has the potential to displace or result in nonunion despite what appears to be adequate reduction and internal fixation. One cause of instability, namely marked displacement at the fracture site, is identified here and should now be included among the risk factors. Early identification of the instability is imperative. Treatment options are modification of reduction techniques, choices of internal fixation devices, and adjustment of postoperative care. The importance of adjusting the treatment to the requirements of an unstable intertrochanteric fracture is emphasized.