Abstract: A head and neck positioner and immobilizer having an over-arm structure that can be reproducibly attached to a couch, either CT or MR imaging couch or a treatment couch as for a LINAC radiosurgery system. The positioner enables adjustable immobilization of the patient's head. The over-arm accepts a graphic reference with fiducials such as points, rods, or diagonals that can reference a selected target position determined from tomographic imaging, such as CT or MRI slices or imaging data, to the over-arm or to the couch onto which the arm is attached. Alternately, a target localizer or positioning device can be attached to the over-arm or to the couch to which the arm is attached for positioning the coordinates of the selected target position as determined using the image scan data with the graphic reference fiducials observed in it.