Tire pressure monitoring system for a vehicle includes sensor units mounted in each tire of the vehicle, each sensor unit being operable to output an RF signal indicative of the pressure in the tire in which it is mounted; a pair of communicator units for receiving signals from said sensor units, said pair of communicator units being provided at different locations on the vehicle; and a control unit connected to said communicator units wherein said control unit is operable to determine which sensor unit is associated with which tire by monitoring the strength of the RF signal received from each respective sensor unit by each communicator unit.