A system and method for monitoring and controlling operation of a disk refiner (32). The method regulates operation in response to a process variable (242) preferably in relation to a setpoint (256). The variable can be temperature, pressure, and/or stock consistency, refiner energy, or a variable based thereon. Volumetric flow rate of stock and/or the flow rate of dilution water can be regulated. Where temperature is used, it preferably is a temperature inside the refiner or adjacent the inlet or outlet. Where pressure is used, it preferably is a pressure inside the refiner or adjacent the refiner inlet (114a, 114b) or outlet. Stock consistency can be determined using a sensor (70) upstream or downstream of the refiner or using a sensed parameter in the refiner.