Abstract: The invention relates to a fibre-optic plug-in connector system (10) comprising an adapter (11), in addition to individual optical plug-in connectors (13), in which a respective optical fibre terminates in a ferrule (23) and which can be respectively inserted into the adapter (11) from two opposing sides to produce an optical connection between the ends of two optical fibres. According to the invention, the adapter (11) has a plurality of parallel guide sheaths (45), which are located next to one another in an adapter housing (12) and into which the optical plug-in connectors (13) comprising their ferrules (23) can be inserted from both sides. To achieve an extremely simple, space-saving construction for a plug-in connector system of this type, the adapter housing (12) is composed of several separate, interconnectable parts (17, 18), between which the guide sheaths (45) are held with a degree of play.