A method of adapting a man-machine interface (20) of an aircraft (50) depending on the functional level of a pilot, the method comprising a plurality of successive steps. Firstly, before starting a mission, the characteristics of said mission and the characteristics and the physiological state of said pilot are determined. Thereafter, during said mission, the state of the mission and the current state of said aircraft together with a current behavior of said pilot are determined and a current functional level of said pilot is estimated. Thereafter, said current functional level of said pilot is compared with reference functional levels, and said man-machine interface (20) is then adapted in order to assist said pilot automatically and in optimum manner in making the pilot aware of the situation, in the pilot's decision-making, or in the actions taken by the pilot depending on the pilot's stress state or work load state.
