A spindle drive and patient positioning system is provided. The spindle drive includes a drive that is operative to drive a spindle nut. An axially transportable spindle is circled by the spindle nut. A catch nut that is not in mutual engagement with the spindle has a predefined distance to the drive. When the spindle nut fails, the spindle is operative to move the catch nut into mutual engagement with the spindle. A switching element is fixed to the catch nut and includes an emergency off switch, which is activated by a switching sensor.