Abstract: An automatic toilet flushing system for use with toilets in either commercial or private dwellings and which comprises a replaceable water tank top or tank lid carrying the major components of the automatic toilet flushing system. In this case, the toilet flushing system is an adaptive system, since it converts a conventional toilet into an automatic flushing toilet. The adaptive system also comprises a pair of infrared light sources and sensors located on forwardly protruding portions of the tank lid. The sensors are located forwardly of the water tank or water chest of the toilet and the timing is adjusted so that raising and lowering of the lid of the toilet seat will not interfere with operation of the sensors. A control circuit is also provided and mounted on the underside of the replaceable water tank cover plate.