Abstract: The craniostatic positioner comprises a pair of plates carried by a transverse yoke and having, one a collimator with a socket for the insertion of the X-ray tube therein, the other a cassette holder with an optical centering device, and a positioning assembly for positioning the patient's head including a headrest, a forehead slider, and an auricolar compass provided with at least one swivelling extension which cooperates with the compass in defining a reference plane containing anatomically definite and selectable points of the skull structure.