An 81-year-old female was treated for a pertrochanteric multifragmentary fracture of the proximal femur with a third-generation Gamma nail. After 3 months she presented herself again with acute pain and inability to bear weight on the leg. Radiographs showed medial migration of the lag screw. She was treated with a total hip arthroplasty, after which she was successfully discharged. In this case report the possible causes of this late and unusual complication are discussed.