The present invention relates to an exhalation valve (10) for a ventilator apparatus for at least partial instrumental respiratory assistance of a patient, comprising a valve housing (14) with a flowpassage (16) which extends along a passage trajectory (D1, D2) defining a local axial, radial and circumferential direction and along which respiratory air can flow through the valve housing (14), wherein the valve housing (14) has a housing-side valve sub-formation with a closed end surface (24) which extends around the passage trajectory (D1) and towards which a mating surface (26) of a valve body (12), movable relative to the valve housing (14) and facing the end surface (24), can be pretensioned by the pretensioning force of a pretensioning device (38) in such a way that the mating surface(26), when subjected to respiratory gas in an exhalation flow direction (E) counter to the pretensioning force of the pretensioning device (38), is removable, with enlargement of an annular gap (42)which is present or can be generated between the end surface (24) and the mating surface (26), from the end surface (24) in a lifting direction (A), such that the flow passage (16) can be flowed through in the exhalation flow direction (E), and flow through the flow passage (16) in a flow direction opposite to the exhalation flow direction (E) can be blocked by the mating surface (26) of the valvebody (12) bearing on the end surface (24), wherein the valve body (12) has a skirt (44) which, when viewing the exhalation valve (10) in a reference state not loaded with intended respiratory flow, surrounding the mating surface (26) and the end surface (24), extends in a circumferential direction and, in the reference state, protrudes from the mating surface (26) past the end surface (24) counter to the lifting direction (A), wherein an annular gap space (46) is provided radially between the skirt (44) and an end portion (22) of the valve sub-formation that has the end surface (24).