The invention relates to a method of adjusting motor parameters in a variable speed drive intended for controlling a synchronous electric motor with permanent magnets M. The method comprises a step of determining the deviations .DELTA.I.sub.D and .DELTA.I.sub.Q between references and measurements of the flux current and motor torque current, a step of calculating a correction value .DELTA.R.sub.S of the stator resistance, a correction value .DELTA.L of the inductance and a correction value .DELTA.K.sub.E of the flux constant of the motor, on the basis of the integral terms of the deviations .DELTA.I.sub.D and .DELTA.I.sub.Q, a step of adjusting the values of the parameters of the motor model on the basis of .DELTA.R.sub.S, .DELTA.L and .DELTA.K.sub.E, a step of formulating the control voltages U.sub.D and U.sub.Q to be applied to the motor M by using the said adjusted values of the motor parameters.