A respiratory mask assembly (10) for delivering breathable gas to a patient includes a frame (20) having a front surface and a rear surface, opposite the front surface, and arranged in use to face the patient. The frame defines an inner wall (28) and an outer wall (30) extending from the rear surface, the inner and outer walls being spaced to define a channel (26) therebetween. A cushion (40) is removably attachable to the frame such that the cushion and frame are repeatably engagable with and disengagable from one another. The cushion includes a side wall (215) to be inserted into the channel (26) of the frame, the side wall having a first interlocking surface (44) that engages a second interlocking surface (33) provided in the channel when the cushion and frame are engaged with one another. The first and second interlocking surfaces interlock with one another to removably attach the cushion to the frame.