Abstract: A multistage centrifugal compressor, comprising a casing having an inlet portion and a compression portion. The inlet portion has an inlet opening gaseously coupled to an evaporator so as to receive a gaseous refrigerant. The inlet and compression portions each have a plurality of gas passages therethrough. The compression portion has an outlet opening that is located at the end of the casing which is opposite the end of the casing having the inlet opening. An electric motor assembly is positioned within the inlet portion of the casing so as to provide a transfer of heat dissipated by the motor assembly to the gaseous refrigerant entering through the inlet opening. The gaseous refrigerant flowing in the inlet opening passes through and about the motor assembly so as to cool the motor assembly.