Abstract: A pneumatic percussor includes a three-way valve that is gated on by a control circuit (50) to gate compressed air from a compressor (10) to a percussor cup (70). The percussor cup (70) is a resilient bellows that is expandable in response to pressurized air that is gated through the three-way valve (28). A variable orifice (62) regulates the air flow to the percussor cup (70). A check valve (60) is connected in parallel with the variable orifice (62) to exhaust air to the atmosphere. The control circuit (50) gates the three-way valve on for a short duration during which the percussor cup (70) is inflated and when the control circuit (50) gates the three-way valve (28) off, the check valve (60) relieves the pressure from the inside of the percussor cup (70) to deflate it. The expansion and contraction of the percussor cup (70) delivers a therapeutic rhythmic action to the portion of the body external to the thoracic cavity thereby stimulating the expectoration of the mucus from the lungs.