Aspergillus is unusual among nosocomial pathogens in several ways: A The inanimate environment is the source of the organisms. The only other nosocomial pathogens for which the environment matters are Legionella and, perhaps, Clostridium difficile. A Outbreaks of nosocomial aspergillosis may include patients infected by more than one spedies. This arises because the outbreaks result from breakdowns in ventilation permitting introduction of a variety of airborne opportunistic fungal spores. a visrtually all nosocomial aspergillosis could be prevented if enough money were available. Unfortunately, this goal requires amounts of money that cannot be rationally allocated. A Nosocomial aspergillosis cases are more highly concentrated in a specific population—immunosuppressed patients—than any other type of nosocomial infection. A Prevention of nosocomial aspergillosis requires the participation of persons—architects, hospital designers, housekeepers, maintenance and engineers—who are not used to the needs involved. The emphasis must be on prevention of nosocomial aspergillosis because the condition is so difficult to diagnose and treat. In the most highly immunosuppressed patients, when there is no pre-existing pulmonary disease, a positive coughed sputum culture in the presence of a pulmonary infiltrate has sufficient sensitivity and specificity to be useful in the clinical diagnosis of invasive pulmonary aspergillosis.1 However, less highly immunosuppressed patients are much more likely to require bronchoscopy or transthoracic aspiration to recover the organism.