The invention relates to a surface replacement prosthesis (1) for the natural femur head (2), comprising an outer spherical surface and an inner receiving space (3) having an inner lateral face and a guide pin (4) on said inner lateral face, which pin projects from the receiving space (3). In order to exclude the risk of micromovements and the resulting destruction of the cement mantle, the guide pin (4) has an out-of-round cross-section at least in sections of its length.
