A spacer device for use with a metered dose inhaler (MDI). The spacer device comprises an aerosol chamber for holding the aerosolized medication sprayed from the MDI. According to one particular design, the aerosol chamber has a forward shell, a rear shell, and an extendable barrel in between. The extendable barrel comprises a flexible plastic sheath that is supported by a coiled wire spring. The spacer device further comprises a mounting bracket to hold the MDI. The mounting bracket holds the MDI such that the spray outlet of the MDI is mated with the aerosol chamber. Also, the assembly is configured such that the aerosol chamber is aligned substantially parallel to the actuator boot of the MDI. During use, the aerosol chamber is folded downward away from the MDI. The aerosol chamber is then extended outward to increase its volume.