Abstract: A uretero-renoscope assembly comprises a first shaft to accommodate an optical system and an auxiliary instrument passage, this first shaft being connected at its proximal end to a housing provided with connections for a light conductor cable and for the infeed or discharge of flushing fluid or the like. The first shaft has a cross-sectional area which decreases in steps in the distal direction, and has a circular cross-section at its proximal end which merges into an oval cross-section at the distal end. A second shaft of circular cross-section can be pushed onto the first, with the first shaft in position in the ureter after withdrawal of the uretero-renoscope, forming a further stepped increase in cross-section and providing a further passage, for example for flushing fluid.