A patient interface for use in delivering breathable gas to a patient, the patient interface comprising: a cushion module comprising a chassis portion and seal-forming structure together forming a plenum chamber pressurisable to a therapeutic pressure of at least 4 cmH 2 O above ambient air pressure, the chassis portion having a width in a direction perpendicular to a sagittal plane of the patient when the patient interface is worn in use, and including a plenum chamber inlet port configured to receive a flow of breathable gas at the therapeutic pressure for breathing by the patient, the seal-forming structure being configured to form a seal with a region of the patient's face surrounding an entrance to the patient's airways, said seal-forming structure having an opening therein such that the flow of breathable gas is delivered to the entrance to the patient's airways, the seal-forming structure being configured to maintain said therapeutic pressure in the plenum chamber throughout the patient's respiratory cycle in use; a vent structure comprised as part of the chassis portion to allow a continuous flow of gases exhaled by the patient from an interior of the plenum chamber to ambient, said vent structure being configured to maintain the therapeutic pressure in the plenum chamber in use; a positioning and stabilising structure to provide a force to hold the seal-forming structure in a therapeutically effective position on the patient's head, the positioning and stabilising structure comprising: a strap configured to be arranged, in use, so that an anterior portion of the strap overlies an anterior surface of the chassis portion across the width of the chassis portion, the strap passes around the sides of the patient's head inferior to the patient's ears, and a posterior portion of the strap overlies a posterior region of the patient's neck, wherein no part of the positioning and stabilising structure is configured to be positioned superior to the patient's ears in use. a cushion module comprising a chassis portion and seal-forming structure together forming a plenum chamber pressurisable to a therapeutic pressure of at least 4 cmH 2 O above ambient air pressure, the chassis portion having a width in a direction perpendicular to a sagittal plane of the patient when the patient interface is worn in use, and including a plenum chamber inlet port configured to receive a flow of breathable gas at the therapeutic pressure for breathing by the patient, the seal-forming structure being configured to form a seal with a region of the patient's face surrounding an entrance to the patient's airways, said seal-forming structure having an opening therein such that the flow of breathable gas is delivered to the entrance to the patient's airways, the seal-forming structure being configured to maintain said therapeutic pressure in the plenum chamber throughout the patient's respiratory cycle in use; a vent structure comprised as part of the chassis portion to allow a continuous flow of gases exhaled by the patient from an interior of the plenum chamber to ambient, said vent structure being configured to maintain the therapeutic pressure in the plenum chamber in use; a positioning and stabilising structure to provide a force to hold the seal-forming structure in a therapeutically effective position on the patient's head, the positioning and stabilising structure comprising: a strap configured to be arranged, in use, so that an anterior portion of the strap overlies an anterior surface of the chassis portion across the width of the chassis portion, the strap passes around the sides of the patient's head inferior to the patient's ears, and a posterior portion of the strap overlies a posterior region of the patient's neck, wherein no part of the positioning and stabilising structure is configured to be positioned superior to the patient's ears in use. a strap configured to be arranged, in use, so that an anterior portion of the strap overlies an anterior surface of the chassis portion across the width of the chassis portion, the strap passes around the sides of the patient's head inferior to the patient's ears, and a posterior portion of the strap overlies a posterior region of the patient's neck, wherein no part of the positioning and stabilising structure is configured to be positioned superior to the patient's ears in use.