A mask assembly includes a mask frame including a lower portion and a neck extending from the lower portion, a cushion provided to the mask frame and adapted to contact a patient's face, a forehead support assembly provided to the neck of the mask frame, the forehead support assembly including a forehead support and a forehead pad provided to the forehead support, and an elbow assembly provided to the mask frame. The neck includes a pair of side walls spaced apart from one another along an entire length of the neck, the side walls providing an open space therebetween along the entire length of the neck that opens towards a front side of the mask assembly. The pair of side walls comprise an upper converging section wherein the pair of side walls converge towards one another in a downward direction.