We report on a 17-year-old man who underwent prophylactic fixation of the incomplete subtrochanteric femur fracture produced by a low-velocity gunshot. The subtrochanteric region is a high-stress site. Therefore, to avoid progression to complete fracture and displacement requiring secondary surgical stabilization, we used a proximal femoral nail for prophylactic fixation of the incomplete subtrochanteric femur fracture. The patient was able to walk and bear weight on the injured side immediately after surgery. At the 1-year follow-up, the patient was pain-free with a full range of motion of his right hip and had a bony union.