Abstract: A plug-in coupling for systems involving pressurized media, where the coupling consists of two connector parts, a housing part (2) and a connector part (4). The connector part (4) can be inserted into a receiving opening (8) of the housing part (2), while it is being sealed, and when it is in a plugged-in condition, it can be locked in place and prevented from being released by means of a locking device (10). The locking device (10) includes a retaining element (12), which is supported on one side of one of the coupling parts, and which retaining element engages—while in the assembled state—a retaining groove (16) of the other coupling part by means of a form-fit or a form- and friction-fit.