An apparatus for the representation of an area on the three-dimensional surface of a patient's body, with a control device which provides three-dimensional coordinates of at least one area to be represented on the surface of the patient's body, wherein the area pre-sets a desired intersection area of a radiation area on the surface of the patient's body, characterized in that at least one projection device featuring a laser is provided, by which the desired intersection area can be projected to the three-dimensional surface of the patient's body on the basis of the provided coordinates, while at least one laser beam generated by the laser can be guided along the contour of the desired intersection area sufficiently rapidly, so that the impression of a closed contour around the desired intersection area results.