a shroud;

a cushion module that engages the shroud, the cushion module including a frame of relatively rigid, polycarbonate material and a full-face cushion of relatively soft, elastomeric material, said full-face cushion being adapted to engage the patient's face generally along nasal bridge, cheek, and chin regions of the patient's face, the frame including an opening and the frame at least partly defining a breathing chamber, the full-face cushion including a base wall provided to the frame, an undercushion layer extending away from the base wall, and a membrane provided to cover the undercushion layer, the undercushion layer being provided in a nasal bridge region of the full-face cushion, the undercushion layer not being provided in at least a part of the chin region;

an elbow connected to the frame in a releasable and rotatable manner, the elbow including a gas washout vent arrangement, and an anti-asphyxia valve, the elbow including a first end portion and a second end portion, the second end portion having a swivel joint adapted to be connected to an air delivery tube, the vent arrangement comprising a vent insert that is adapted to be supported within an outlet opening in the elbow, the vent insert having a plurality of vent holes, the elbow including a port that is selectively closed by a flap portion of the anti-asphyxia valve depending on the presence of pressurized gas, the port being positioned between the swivel joint and the vent arrangement; and

headgear to maintain the mask system in position on the patient's face, wherein:

the first end portion of the elbow including a distal end releasably inserted into the opening of the frame with a snap-fit, thereby creating a retention structure to retain the elbow with the frame, whereby the retention structure between the elbow and the frame also maintains the shroud in engagement with the frame, the shroud and the frame being structured to prevent relative rotation when the elbow is snap-fitted to the frame, and

the shroud includes an interfacing structure configured and shaped to hold the cushion module in an operative position with respect to the patient's face, the interfacing structure being positioned along an inner side of the shroud that contacts the frame of the cushion module.