Parasites are important determinants of ecological dynamics. Despite the widespread perception that parasites (in the broad sense, including microbial pathogens) threaten species with extinction, the simplest deterministic models of parasite dynamics (i.e. of specialist parasites with density-dependent transmission) predict that parasites will always go extinct before their hosts. We review the primary theoretical mechanisms that allow disease-induced extinction and compare them with the empirical literature on parasitic threats to populations to assess the importance of different mechanisms in threatening natural populations. Small pre-epidemic population size and the presence of reservoirs are the most commonly cited factors for disease-induced extinction in empirical studies.