Abstract: A wax guard for a hearing aid is mushroom-shaped, having a cross passage through its head which intersects an axial passage in its stem. The axial passage contains an acoustic filter terminating the axial passage in its characteristic impedance. The cross passage is semi-circular in section to reduce the projection of the guard into an ear canal and the total area of the two branches of the passage exiting from the axial passage is equal to that of the axial passage. The guard removably snap fits into a metal ring glued into the outlet port of the hearing aid.