A respiratory mask assembly includes a frame, a forehead support, and an adjustment mechanism including a single finger-operated push button to allow selective adjustment of the forehead support relative to the frame. The frame includes a support arm and a housing provided to a free end of the support arm. The housing includes a front side including a closed configuration, a rear side, and a receiving space extending from the rear side and structured to slidably receive a slider of the forehead support. The forehead support is slidably mounted for linear movement in a direction which is substantially perpendicular to a longitudinal axis of the support arm. The single finger-operated push button includes a portion that extends through an opening provided in a top side of the housing.