A mask assembly (10) is provided for delivering gas to a patient that includes a mask body (12) and a breathing circuit interface (16). The mask body includes an opening (13) for reception of the gas and includes a seal structure (20) for sealingly engaging with the face of the patient and surrounding at least the nose and mouth of the patient. The breathing circuit interface includes a first portion (17) rotatably connected with the mask body and a second portion (19) that is constructed and arranged to releasably connect with a conduit (18) for delivering the gas to the patient through the opening.