Shoulder prosthesis, including a stem provided to be inserted into a canal of the humerus shaft, a neck and a head supported by the neck. The neck is provided with two holes (1, 2) for anchoring screws (1a, 2a), namely a first hole (1) for a lateral anchoring screw (1a) and a second hole (2) for an anterior anchoring screw (2a). The lateral anchoring screw is provided to attach a first tubercle laterally to the neck and the anterior anchoring screw is provided to attach a second tubercle anterior to the neck. A system for implanting a shoulder prosthesis, comprises a targeting arm attachable to the neck of the prosthesis and is provided with guide means for guiding anchoring screws (1a, 2a) to be screwed into at least a lateral hole (1) and an anterior hole (2) in the neck. The targeting arm is also provided for holding a trial prosthesis.