Abstract: To improve the reliability of a process for determining the position of a body part in which bone screws are screwed into the bone of the body part in question, each bone screw is provided with a radiation emitter or radiation receiver. A number of fixed receivers or emitters are used as appropriate to receive radiation from the bone screw transmitters or direct radiation towards the bone screw receivers. The radiation direction and/or radiation propagation time and/or radiation field strength or frequency is used to determine the position of each radiation emitter or receiver. A system for determining position based on this procedure and bone screws which can be used therefor are also disclosed.