The history of airborne nosocomial infections is reviewed, and current beliefs about such infections are placed into their historical context. Possible sources, both animate and inanimate, of airborne nosocomial infections in the hospital environment are identified. Viruses, bacteria, and fungi that have been important causes of airborne nosocomial infections in the past are discussed, and examples of key studies that have confirmed an airborne route of transmission are presented. Where relevant, measures that have been used to control airborne transmission of nosocomial pathogens are discussed. Although outbreaks of airborne nosocomial infection have been uncommon, airborne transmission appears to account for about 10% of all endemic nosocomial infections.