In the current climate of cost containment and quality control, nosocomial infection is a worrisome adverse event in hospital care. Hospitalised patients require care for increasingly severe illnesses, and are therefore more susceptible to infection, especially by opportunistic micro-organisms. It is thus necessary to accurately assess and adjust for the severity of the underlying illness in studies of risk factors involved in nosocomial infections. The appearance of new diagnostic and therapeutic techniques provides novel opportunities for infection control and represents a constant challenge to hospital systems. The continuous selection of resistant flora, together with the identification of new pathogens, calls for a reconsideration of hospital policies regarding the dispensation of antibiotics. Epidemiological surveillance continues to be the most important aspect of attempts to monitor infection control programmes, and to identify changes in risk factors that may increase the infection rate. Among the major challenges now facing the infection control practitioner is the use of nosocomial infection rates as an indicator of quality of care. Awareness of infection statistics would serve as a stimulus to the prevention and control of infection, but would be useless if not accompanied by adequate systems to guarantee the comparability of data from different studies and centres. Suitably sensitive and specific surveillance systems should be developed, and the use of site-specific and procedure-specific infection rates adjusted for the patient's intrinsic risk should be encouraged.