There were 42900 institution-beds in long-term care facilities for elderly persons in Norway in 2000. This is twice as many as in 1984. Of those living in an elderly people's care institution 77% were above 80 years. To determine the magnitude and distribution of nosocomial infections in such institutions, the Norwegian Institute of Public Health initiated a surveillance system. The system is based on two annual one-day prevalence surveys recording the four most common nosocomial infections: urinary tract infections, lower respiratory tract infections, surgical-site infections and skin infections, as well as antibiotic use. All long-term care facilities were invited to participate in the four surveys in 2002 and 2003. The total prevalence of the four recorded nosocomial infections varied between 6.6 and 7.3% in the four surveys. Nosocomial infections occurred most frequently in the urinary tract (50%), followed by infections of the skin (25%), of the lower respiratory tract (19%) and of surgical sites (5%). The prevalence of nosocomial infections was highest in rehabilitation and short-term wards, whereas the lowest prevalence was found in special units for persons with dementia. In all the surveys the prevalence of the four recorded nosocomial infections was higher than the prevalence of patients receiving antibiotics. The frequency of nosocomial infections in such facilities highlights the need for nosocomial infection surveillance in this population and a need to implement infection control measures, such as infection control programmes including surveillance of nosocomial infections.