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 ΔID and ΔIQ between references and measurements of the flux current and motor torque current, a step of calculating a correction value ΔRS of the stator resistance, a correction value ΔL of the inductance and a correction value ΔKE of the flux constant of the motor, on the basis of the integral terms of the deviations ΔID and ΔIQ, a step of adjusting the values of the parameters of the motor model on the basis of ΔRS, ΔL and ΔKE, a step of formulating the control voltages UD and UQ to be applied to the motor M by using the said adjusted values of the motor parameters.