The impact of nosocomial viral disease, in terms of morbidity, mortality, and health care expenditures, should not be underestimated. Respiratory viruses, in particular, account for a substantial proportion of all nosocomial infections, especially among pediatric patients and the institutionalized elderly. The immunocompromised, very young, and chronically ill patients in hospitals are unusually vulnerable to serious viral illness. The emerging technology of rapid viral diagnosis will allow more timely and accurate recognition of viral infections, even in the smaller hospital with limited laboratory resources. Early recognition of viral diseases should, in turn, permit us to institute, and further evaluate, specific measures for their control. Appreciation of the epidemiology and transmission of these viruses will provide the framework for successful infection control strategies.