The invention relates to a cooling device for an electric motor comprising at least one closed capillary tube (6), within which a cooling fluid (13, 14) is located and which is introduced into an opening (5) of a lamination stack (1) of the electric motor in such a way that the capillary tube (6) is connected to the lamination stack (1) so as to conduct heat and partially projects out of the lamination stack (1), such that the capillary tube (6) has a cold end (7) disposed outside the lamination stack (1) and a hot end (7) disposed inside the lamination stack (1). The cooling fluid (13, 14) and the degree of filling of the capillary tube (6) with the cooling fluid (13, 14) is chosen in such a way that, in operation of the electric motor, an input (17) of heat from the lamination stack (1) into the capillary tube (6) leads to evaporation of the cooling fluid (13, 14), and the cold end (8) of the capillary tube (6) can be cooled in such a way that the vapour (14) produced during the evaporation condenses and the heat input (17) into the capillary tube (6) can be dissipated (18) out of the capillary tube.