A guide clamp for clamping a femur and guiding placement of a guide wire relative to the femur. The guide clamp includes a body supporting a pair of clamping surfaces at the end of a pair of clamping arms that are spring-biased to move with respect to each other into a closed position to grip the femur. Defined by the body is a guide opening that guides insertion of the guide pin once the femur has been gripped. One of the clamping arms of the guide clamp may have proximal and distal portions that are slidably adjustable with respect to each other to allow a controlled repositioning of the guide opening with respect to the femur. The guide clamp may also include an engagement member which is supported by the body of the clamp and is capable of advancing into abutting contact with the head of the femur.