A full-face mask system for delivery of a supply of gas at positive pressure to a patient for medical treatment includes a shroud, a cushion module adapted to form a seal with the patient's nose and mouth, an elbow, and headgear. The cushion module includes a frame and a cushion. The frame includes an opening that releasably receives a distal end of the elbow with a snap-fit, wherein an inner edge of the opening and the distal end of the elbow together form a retention structure to retain the elbow to the frame. The elbow has an exterior surface rotatable relative to a bearing surface formed on an inner circumferential surface of the opening, the elbow having an annular protrusion that abuts the frame of the cushion module when the distal end of the elbow is fully inserted into the opening. The retention structure maintains engagement between the shroud and the frame.