The present invention pertains to a valved holding chamber suitable for use in an aerosol medication delivery system. The valved holding chamber includes a housing and a mouthpiece coupled to the housing. A one-way valve assembly is coupled to the housing, the mouthpiece, or both so that fluid flows in a first direction from the housing to the mouthpiece passes through the valve assembly but does not pass back into the housing. The valve assembly includes a conical flange disposed such that the conical flange tapers in the first direction to smooth the fluid flow in the first direction toward the patient. In a further embodiment, the mouthpiece includes an exhaust port defined in a conical collar portion of the mouthpiece, and an exhaust valve element is disposed over the exhaust port to provide a one-way flow of fluid from within the mouthpiece to ambient atmosphere via the exhaust port.