Various epidemiological investigations of outbreaks and sporadic cases have clearly demonstrated that the consumption of contaminated food is responsible for a high proportion of listeriosis cases and Listeria monocytogenes has been increasingly recognized as an important foodborne pathogen over the last 15 years. The emergence of listeriosis is the result of complex interactions of different factors: medical progress which increases the lifespan and allows immunodeficient people to survive, expansion of the food industry and cold storage systems as well as changes in food habits. None of these factors on its own is entirely responsible. Considerable research has attempted to characterize the organism, define the magnitude of the public health problem and its impact on the food industry, identify the risk factors associated with the disease, and devise appropriate control strategies. Nevertheless, a number of crucial questions remains incompletely elucidated (extent of the foodborne transmission of listeriosis, health status of apparently "healthy patients" with the possible role of an intercurrent infection or genetic susceptibility, how to distinguish highly virulent from less virulent strains of L. monocytogenes, factors contributing to the emergence of outbreaks, the possible role of healthy carriers in the epidemiology of listeriosis, etc.). To investigate the complexity of listeriosis requires the close collaboration of clinicians, epidemiologists, clinical and food microbiologists, food scientists and the food industry. A large amount of data has been accumulated during the past 10 years but more research is required to elucidate the epidemiology of the disease and the virulence of the causative agent.