The invention relates to a hip prosthesis comprising a straight shaft (1) to be inserted into the femur. The proximal part (6) of said shaft to be inserted into the metaphyseal region of the femur comprises at least one projecting fin (8) having a medially steep flank (23) on the front and rear sides. Said fin (8) deviates away from the longitudinal direction (27) of the shaft (1) and is upwardly inclined towards the femoral neck (2), at least over part of its length. In this way, when the shaft is driven into the bone, the bone substance surrounding the fin (8) thickens and is able to absorb higher forces. The height of the fin (8) decreases from the medial flank thereof (23) to the lateral edge (25) thereof.