Abstract: A system and method for initializing and calibrating a fiber optic pressure transducer so that a measured intensity of light which varies as a function of pressure can be accurately translated to the value of pressure which produces that value of light intensity. The transducer includes an enclosed sensor tip having a diaphragm which is exposed to atmospheric pressure on the inside and the pressure to be determined on the outside as measurements are taken, the resulting pressure differential producing a related attenuation in light intensity. Calibration according to the present invention is performed by exposing the diaphragm to atmospheric pressure on the outside and sub-atmospheric pressure on the inside while transmitting light through the fiber in the usual manner. The sub-atmospheric pressure is changed gradually as simultaneous measurements are made of the intensity of light returned through the fiber and the actual value of the sub-atmospheric pressure at a number of discrete times.