Abstract: An automatic mirror positioning system is intended for tractor-trailer vehicles such as a tractor provided with a semi-trailer. The tractor includes a fifth wheel used to couple the trailer to the tractor. The system includes an angle detection unit to measure a relative angular pivot between the tractor and the trailer, a computer for interpreting data received from the detection unit, and a mirror assembly which includes a rotatable mirror which is operated by the signals received from the computer, whereby the system modifies the positions of the exterior rearview mirrors of the tractor in view of the relative position of the tractor and the trailer in order that the driver can view the sides and the rear corners of the trailer for any angle defined between the tractor and the trailer.