The prevention and surveillance of nosocomial bacteria (NB) are priorities due to the high incidence of infections (7% of nosocomial infections, according to the 1996 national prevalence survey) and the high mortality rate they cause. This is why the Microbiology Network of CCLIN Paris-Nord launched a program in 1994 to monitor HAI using data from laboratories across the region. This program was designed, on the one hand, to collect multicenter data—which is rare in France—and, on the other hand, to provide healthcare facilities with a tool enabling them to assess their own epidemiological situation in order to help them develop prevention strategies. (Adapted summary of the text)