Method for operating a trailer maneuvering assistance system of a motor vehicle, in which a maneuvering operation of a tandem consisting of a motor vehicle and a trailer into a target position is supported by means of the trailer maneuvering assistance system, comprising the steps of: - detecting the trailer by means of a sensor device of the motor vehicle when the trailer is coupled to the motor vehicle and transmitting to an evaluation device of the trailer maneuvering assistance system sensor data concerning the detected trailer; - determining, by means of the evaluation device, dimensions of the trailer in the longitudinal direction, transverse direction, and vertical direction of the trailer on the basis of the transmitted sensor data; - supporting the maneuvering operation of the tandem into the target position, taking into account the determined dimensions of the trailer, characterized in that on the basis of the determined dimensions, a three-dimensional model the trailer is created and displayed, so that a real displayed image of the trailer is semi-transparently overlaid, and a user request is issued that the respective outer edges of the three-dimensional model of the trailer be moved by means of an operating device of the motor vehicle until the outer edges coincide with the outer edges of the real image of the trailer, wherein the outer edges are shifted in accordance with a detected actuation of the operating device. motor vehicle, in which a maneuvering operation of a tandem consisting of a motor vehicle and a trailer into a target position is supported by means of the trailer maneuvering assistance system, comprising the steps of: - detecting the trailer by means of a sensor device of the motor vehicle when the trailer is coupled to the motor vehicle and transmitting to an evaluation device of the trailer maneuvering assistance system sensor data concerning the detected trailer; - determining, by means of the evaluation device, dimensions of the trailer in the longitudinal direction, transverse direction, and vertical direction of the trailer on the basis of the transmitted sensor data; - supporting the maneuvering operation of the tandem into the target position, taking into account the determined dimensions of the trailer, - detecting the trailer by means of a sensor device of the motor vehicle when the trailer is coupled to the motor vehicle and transmitting to an evaluation device of the trailer maneuvering assistance system sensor data concerning the detected trailer; - determining, by means of the evaluation device, dimensions of the trailer in the longitudinal direction, transverse direction, and vertical direction of the trailer on the basis of the transmitted sensor data; - supporting the maneuvering operation of the tandem into the target position, taking into account the determined dimensions of the trailer, characterized in that on the basis of the determined dimensions, a three-dimensional model the trailer is created and displayed, so that a real displayed image of the trailer is semi-transparently overlaid, and a user request is issued that the respective outer edges of the three-dimensional model of the trailer be moved by means of an operating device of the motor vehicle until the outer edges coincide with the outer edges of the real image of the trailer, wherein the outer edges are shifted in accordance with a detected actuation of the operating device. on the basis of the determined dimensions, a three-dimensional model the trailer is created and displayed, so that a real displayed image of the trailer is semi-transparently overlaid, and a user request is issued that the respective outer edges of the three-dimensional model of the trailer be moved by means of an operating device of the motor vehicle until the outer edges coincide with the outer edges of the real image of the trailer, wherein the outer edges are shifted in accordance with a detected actuation of the operating device.