The method involves placing the body part in the acquisition region of a navigation system supported by at least two cameras (5,6), which detect 3-dimensional spatial positions of light markings (3) supported by a computer, producing light markings on the surface of the body part whose three-dimensional positions are defined by the navigation system and determining position data for the body part using the position data for the light markings. Independent claims are also included for the following: an arrangement for referencing or recording a patient or a body part of a patient.