An obstacle detection system, particularly for assisting car parking that comprises a control unit and a plurality of sensors, which comprise emitters-receivers for emitting an ultrasonic signal and for receiving an echo signal reflected by at least one obstacle and an evaluator for the parametric evaluation of the received echo signals, the evaluator comprising a polling module suitable to determine, for each sensing, the number of times for which the received signals are repeated and to reject the signals that are repeated for a number of times that is lower than a preset number.