The assembly (10) for admitting combustion air to the engine of a motorcycle comprises: an air filter (12); a housing (11) for mounting at the top portion of the motorcycle and forming a support for the air filter (12); an air inlet module (13) fitted to the housing and including at least one movable shutter (131, 131'); control means for controlling the movements of the shutter (131, 131'); and assembly means (17, 171-174) for assembling the assembly at the top portion (21) of the motorcycle. The air filter (12) is generally annular and subdivides the inside volume of the housing (11) into a radially inner chamber and a radially outer chamber. The radially inner chamber is fed with air through the air inlet module (13), while the radially outer chamber forms, around the air filter (12), a chamber for stabilizing the flow of air downstream from the filter.