Abstract: An account is given of a method for monitoring of the position of patients and/or radiation units in which a first position is taken by a camera and stored and comparison between the stored position and the second position taken by the camera takes place. The first position taken by the camera and able to be reproduced as a positive or negative image is changed into a negative image and is so put into line with the second position, taken by the camera, in the positive or negative image that all image points of the first position are able to be seen in a first color contrast and that all image points of the second position are able to be seen in a second color contrast and in that all image points which are in line are able to be seen in a third color contrast. The second position of the patient and/or of the radiation unit is changed till only the third color contrast is to be seen.