A method for creating a vertical trajectory profile of an aircraft by optimization of a criterion representative of a flight cost, comprises: performing a first iterative computation of a profile free of altitude constraints as long as a condition dependent on the criterion is not reached, replacing each free level of the constraint-free profile with a permitted level so as to generate an initial constrained profile comprising a plurality of permitted levels, and, for each level, an altitude change point and a plurality of speeds, and performing a second iterative computation of a profile in which the altitude levels to be reached remain constant, equal to the initial permitted levels of the initial constrained profile, as long as a condition dependent on the criterion is not reached.