PURPOSE : To establish the incidence and type of knee fractures, injury of knee ligament associated with ipsilateral femoral shaft fractures. What is the most common mechanism of these combined injuries? MATERIALS AND METHODS : From March 1995 to February 1999, evaluation of one hundred and twenty consecutive patients with fracture of the femoral shaft showed fractures and injuries of the ligaments of the ipsilateral knee in thirty-five(29%) of them. Of those thirty-five, nineteen patients had injured their knees and femoral shaft fractures by the dashboard injury. Twelve injuries were caused in a motor cycle accident, and two patients occurred in pedestrians struck by cars. Two injuries were caused by falls. RESULTS : There were twenty fractures of th knee and fifteen injuries of the ligament. Seventeen of the twenty fractures were in the patella, two in the bicondyle of the proximal tibia and one in the lateral condyle of the proximal tibia. Eleven of seventeen fractures of the patella were open fractures. Of fifteen injuries of the ligament, there were six posterior cruciate ligament tears (including 2 partial tears and 1 avulsion fracture), three posterior cruciate ligament tears with medial or lateral collateral ligament disruption , three anterior cruciate ligament tears(2 tibial spine fractures and 1 partial tear), two lateral collateral ligament disruptions and one medial collateral ligament tear. The locations of femoral shaft fracture were proximal in four patients, middle in thirty, and distal in one patient. CONCLUSION : We conclude that there is a high incidence of ipsilateral fracture of the patella and posterior cruciate ligament tears in patients with femoral shaft fractures. The dashboard injury is the most common mechanism of the ipsilateral knee fractures and ligament tears with femoral shaft fractures.