The invention relates to a magnetic sensor for determining the position of a part (2) movable firstly in rotation over a limited angular stroke by virtue of a rotary movement (R), and secondly in translation along a translation axis (X) and over a limited linear stroke, this sensor including both a magnetized target (3) mounted on and fastened to the movable part (2) and taking the form of a radially-magnetized part-cylinder having an axis of symmetry coinciding with the translation axis (X) and also a system (5) for measuring the magnetic field of the magnetized target to determine the position of the target in three dimensions. According to the invention, in order to determine the position and the orientation of the target, the system (5) acts at a single point to measure the direction of the magnetic field in two orthogonal planes, one of which (P1) is normal to the rotary movement (R) and the other of which (P2) is normal to the movement in translation (X).