A control system for an internal combustion engine having an exhaust gas recirculation device for recirculating a part of exhaust gases to an intake system of the engine is disclosed. An estimated exhaust gas recirculation amount is calculated using a neural network to which at least one engine operating parameter indicative of an operating condition of the engine is input. The neural network outputs an estimated value of an amount of exhaust gases recirculated by the exhaust gas recirculation device. At least one engine control parameter for controlling the engine is calculated based on the estimated exhaust gas recirculation amount.