Airborne transmission of Pneumocystis sp. from host to host has been demonstrated in rodent models and several observations suggest that interindividual transmission occurs in humans. Moreover, it is accepted that the Pneumocystis organisms infecting each mammalian species are host specific and that the hypothesis of an animal reservoir for Pneumocystis jirovecii (P. jirovecii), the human-specific Pneumocystis species, can be excluded. An exosaprophytic form of the fungus cannot be strictly ruled out. However, these data point toward the potential for the specific host to serve as its own reservoir and for Pneumocystis infection in humans as an anthroponosis with humans as a reservoir for P. jirovecii. This review highlights the main data on host-to-host transmission of Pneumocystis in rodent models and in humans by the airborne route and provides a rationale for considering the occurrence of nosocomial infections and measures for their prevention