The invention relates to a spindle drive for a diagnostic or therapeutic device. In an advantageous embodiment, the spindle drive comprises a drive (20) , a spindle nut (19) driven by the drive (20), a spindle (18) circled by the spindle nut (19), and a catch nut (10) . The catch nut (10) is constructed such that, while the spindle nut (19) is intact, it is not in mutual engagement with the spindle (18) and assumes a predefined distance to the drive (20) . If the spindle nut (19) fails, however, it is brought by axial movement of the spindle (18) into mutual engagement with the spindle (18). Further, a switching element is included, which is fixedly connected to the catch nut (10) . The catch nut (10) can be moved axially within predefined motional limits. In addition, an emergency off switch (5) is included, which can be activated by a switching sensor, the switching element actuating the switching sensor when the catch nut (10) is moved axially relative to the drive (20) by axial movement of the spindle (18).
