A mask system for use between a patient and a device to deliver a breathable gas to the patient includes a mouth cushion, a pair of nasal prongs, an elbow, and a headgear assembly. The mouth cushion is structured to sealingly engage around an exterior of a patient's mouth in use, and the pair of nasal prongs are structured to sealingly communicate with nasal passages of a patient's nose in use. The elbow delivers breathable gas to the patient. The headgear assembly maintains the mouth cushion and the nasal prongs in a desired position on the patient's face. The headgear assembly provides a substantially round crown strap that cups the parietal bone and occipital bone of the patient's head in use.