System and method for controlling insertion of a tracheal tube in a patient, comprising at least two electrodes adapted to be coupled to the patients chest for providing impedance measurements, a measuring instrument for performing the impedance measurement, said instrument also being provided with storage means for storing a first data set representing chosen characteristics of the impedance change during a first measurement, and evaluation means for comparing the first data set with a second data set representing the characteristics of a second impedance measurement, for evaluating the difference between said measurements and providing an evaluation signal, said first and second data sets representing impedance variations measured during lung inflation with and without an inserted tracheal tube.