The present invention relates to a stereo microscope (20) with a first and a second main beam path (21, 22), the spacing of which defines a stereo base (23), wherein an axis of the microscope (24) extends through the middle of the stereo base (23) parallel to the main beam paths (21, 22), and with an optical beam splitter device (30) for producing an assistant beam path (31) and a documentation beam path (32), wherein the direction of the assistant beam path (31) in a first position is rotated by 180° to the direction of the assistant beam path (31) in a second position of the beam splitter device (30), and the decoupled documentation beam path (32) in both positions of the beam splitter device (30) is in each case perpendicular to the decoupled assistant beam path (31), and wherein in both the first and second positions of the beam splitter device (30) the assistant beam path (31) can in each case be decoupled at least from the first main beam path (21) and the documentation beam path (32) can in each case be decoupled at least from the second main beam path (22).