Interlocking screws have extended the use of intramedullary nail into comminuted, unstable fractures, from subtrochanteric to supracondylar region of the femoral fractures. But it is still controversial whether dynamization is necessary in the course of treatment. Forty-nine femoral fractures treated with interlocked intramedullary nailing were investigated. Static nailing was converted to dynamic one in 33 femurs with removal of the proximal or distal locking screws. The rest were kept in static nailing. In 19 out of 33 cases with dynamization, there was average 6.0mm of telescoping after dynamization. Average 3.8mm of telescoping was seen in 15 out of 25 cases with removal of the distal locking screws while average 14.3mm in 4 out of 8 cases with removal of the proximal locking screws. There were 4 cases of breakage of distal locking screws without dynamization. Union was achieved in 45 fractures of the 49 cases. Dynamization improves fracture healing by reducing fracture gap and increasing axial compression. Dynamization is necessary in selected cases, especially fractures with a large fracture gap after static nailing and fractures that failed in filling the fracture gap even after some time postoperatively, and it is even more necessary in order to prevent breakage of locking screws in such cases.