A treatment-diagnostic apparatus has a positioning device with a positioning plate for the treatment and/or examination subject that is adjustable at a base and is transparent for radiation in at least one region. The positioning plate, with reference to the base, is mounted so as to be adjustable at least along its longitudinal axis and is mounted at the base so as to be adjustable in height, as well as around three spatial axes x, y, z. Due to the versatile adjustability, such an apparatus meets the demands for an angiographic diagnostic and/or therapy as well as for surgical procedures.