1. A method for referencing or registering a patient or a patient body part in a camera-assisted, medical navigation system comprising the following steps: the patient body part to be referenced is brought into the detecting range of a navigation system assisted by at least two cameras, this navigation system detecting with computer support the three-dimensional, spatial positions of light marks, light marks are generated on the surface of the part of the body to be referenced by means of a light beam, the three-dimensional position of the light marks being determined by the camera-assisted navigation system, the three-dimensional position of the surface of the part of the body to be referenced is determined by means of the positional data for the light marks.