We report an uncommon complication following interlocking intramedullary nailing of the femur: delayed femoral neck fracture after 5 months of unevenful postoperative course. He was a 47-year-old laborer with good quality of bone, nevertheless he sustained femoral neck fracture after minor fall on the ground. We thought that loss of bone elasticity caused by interlocked nail in the whole femoral shaft including intertrochanteric portion made stress concentration on the femoral neck to develop a fracture with minor magnitude of traumatic force.