In permanent magnet synchronous machines (PMSM), depending on the machine application, different types of permanent magnets (PM) can be used. The most common PMs are ferrite magnets, neodymium iron boron magnets (NdFeB), and samarium cobalt magnets (SmCo). The selection of a suitable magnet for a particular machine design depends on the magnet properties: remanence, conductivity, mechanical rigidity, losses, and demagnetization characteristics. Usually, the possibility of hysteresis losses in PM materials is neglected. In this paper, however, it is demonstrated that possible hysteresis losses have to be evaluated in the machine design. It is shown by measurements and simulations that in some machine designs, hysteresis losses in NdFeB, SmCo, and ferrite magnets can be a source of significant additional ac losses that may lead to too high PM operating temperatures and a reduction in the machine efficiency.