The proper level of transection of the femoral neck for hip arthroplasty can be ascertained by using the proximal tip of the intact greater trochanter as a reference point. A transverse line projected medially from this point will cross the true level of the center of rotation of the femoral head for that hip. Placement of a trial prosthesis in accordance with this level will locate the point at which the femoral neck should be cut. By placing the femoral component so that its center of rotation is bisected by the same line, the level of the calcar flange can be marked on the neck of the femur. This is the level at which the femoral neck should be cut.