Much attention has been directed towards nosocomial transmission of viruses as a result of clear evidence of patient-to-staff and staff-to-patient transmission of the blood-borne viruses HIV and hepatitis B virus. Although the relatively long incubation periods of these viruses, together with the frequency of asymptomatic infections, renders problems for surveillance it has been possible to study modes of transmission and levels of risk over a number of years. Information on trends of incidence of other nosocomial virus infections has been difficult to obtain for a number of reasons. Often, an outbreak in the health care setting parallels an epidemic in the community. Although it may be possible to define nosocomial transmission from recording dates of onset of illness relative to admission date and, at times, demonstrate circulation of a common strain by molecular techniques, the relative contributions of patient-to-staff and staff-to-patient transmission may be difficult to clarify. In this review, details are presented of the major viruses associated with nosocomial transmission with examples of infections to and from staff where these have occurred. The major defences against patient-to-staff and staff-to-patient transmission are awareness of potential risks, education and adherence to infection control policies, immunization of staff, effective decontamination and sterilization and the adoption of 'Universal Precautions' in patient care. In addition, there may be occasions when additional measures should be considered including isolation, cohorting and the use of specific chemo- and immunoprophylaxis.