The invention relates to a focusing and positioning ancillary device for a particle-optical scanning microscope, a particle-optical scanning microscope including a corresponding positioning aid, and a method for focusing and positioning an object in a particle-optical scanning microscope. The focusing and positioning ancillary device includes an illuminating device, a camera, a display and a control unit. The illuminating device produces a collimated or focused light beam at an angle to the particle-optical beam axis which intersects the particle-optical beam axis at a predetermined position. The camera is sensitive to the wavelength of the light beam and records an image of the object, which is positioned on the object table, at a second angle to the particle-optical beam axis. The control unit produces an image captured by the camera on the display together with a marking which indicates the position of the particle-optical beam axis in the image.