A medicament delivery system comprises a nebulizer device, an open-faced mist chamber-defining element having a tubular input/output port, a tubular inhalation port connecting to the output port of the mist chamber-defining element, and a sealed unit dose ampoule adapted to fit within the mist chamber-defining element. The nebulizer device includes an ultrasonic transducer responsive to applied electrical energy to generate ultrasonic energy, an ultrasonic transmission horn between an input energy surface at an input end and an energy delivery surface at an output end. The sealed unit dose ampoule can be placed directly into the nebulizer device and acts as both the dose cup and baffle, so that the chance of spillage of drug and the number of components to be cleaned are minimized.