1. A method for detecting the three-dimensional position of an examination instrument inserted into a body region, on which instrument there are provided at least three radiatively opague markings whose mutual geometric arrangement is known, by using a recording device for recording radiation images with the aid of a radiation source and a radiation receiver, the method comprising the steps of: recording at least one two-dimensional projection image of the body region, determining positions (u i, v i ) of the at least three radiatively opaque markings shown in the projection image, and determining spatial coordinates (x i, y l, z l ) of the at least three markings in a coordinate system of the recording device with the aid of the positions (u i, v l ) and a projection matrix belonging to the projection image, taking into account of the known mutual geometric arrangement of the markings.