A suction control regulator for use with a medical suction catheter wherein the regulator includes a rigid molded body attached to a flexible suction catheter at its front and connectable to a source of suction at its rear. An intermediate portion is located between the front and rear portions to act as a means for regulating suction. The intermediate portion includes an outwardly extending stem with an inner passage, the stem terminating in an oval-shaped contoured flange which generally conforms in shape to the contour of the user's thumb. A resilient boot is mounted on the stem and the boot includes a flat diaphragm top suspended and free floating above the stem flange when positioned in a normally open to atmosphere non-suction applied position. The diaphragm top is depressible downward by the thumb to conform to the shape of the flange to seal off the inner passage to close the passage to atmosphere to a suction applied position. The diaphragm protects the user's thumb from contact with aspirated secretions during operation of the device.