Method for determining the rotation speed of at least one supercharger which compresses the sucked air in an internal combustion engine; the control method, during the normal operation of the internal combustion engine, comprises the steps of: detecting, by means of a microphone, the intensity of a sound signal generated by the rotation of the supercharger; determining a frequency content of the sound signal generated by the rotation' of the supercharger; identifying the frequencies with maximum amplitude within the frequency content of the sound signal generated by the rotation of the supercharger; recognizing the frequencies with maximum amplitude which are each other's multiples or submultiples; and determining the rotation speed of the supercharger using exclusively the frequencies with maximum amplitude, which are each other's multiples or submultiples; the method is characterized in that it comprises the further steps of: determining a research interval which is centered on the previous value of the rotation speed of the supercharger and has a semi-amplitude which is equal to the maximum acceleration possible multiplied by the time interval which elapses between the instant in which the previous value of the rotation speed of the supercharger has been determined and the instant in which the new value of the rotation speed of the supercharger is determined; and researching the new value of the rotation speed of the supercharger using the frequencies with maximum amplitude which are each other's multiples or submultiples exclusively within the research interval. detecting, by means of a microphone, the intensity of a sound signal generated by the rotation of the supercharger; determining a frequency content of the sound signal generated by the rotation' of the supercharger; identifying the frequencies with maximum amplitude within the frequency content of the sound signal generated by the rotation of the supercharger; recognizing the frequencies with maximum amplitude which are each other's multiples or submultiples; and determining the rotation speed of the supercharger using exclusively the frequencies with maximum amplitude, which are each other's multiples or submultiples; the method is characterized in that it comprises the further steps of: determining a research interval which is centered on the previous value of the rotation speed of the supercharger and has a semi-amplitude which is equal to the maximum acceleration possible multiplied by the time interval which elapses between the instant in which the previous value of the rotation speed of the supercharger has been determined and the instant in which the new value of the rotation speed of the supercharger is determined; and researching the new value of the rotation speed of the supercharger using the frequencies with maximum amplitude which are each other's multiples or submultiples exclusively within the research interval. determining a research interval which is centered on the previous value of the rotation speed of the supercharger and has a semi-amplitude which is equal to the maximum acceleration possible multiplied by the time interval which elapses between the instant in which the previous value of the rotation speed of the supercharger has been determined and the instant in which the new value of the rotation speed of the supercharger is determined; and researching the new value of the rotation speed of the supercharger using the frequencies with maximum amplitude which are each other's multiples or submultiples exclusively within the research interval.