We report the findings of the study of 4185 food samples and 958 environmental samples collected in Italy in the period 1990-1999 and tested for the presence of Listeria monocytogenes. The strains isolated were biochemically and serologically characterised. We found a fairly high percentage of L. monocytogenes contamination in food (12.8%), whereas the level of contamination was lower in the environment (environment and work surfaces in food processing plants) (6.1%). Serotyping showed a prevalence of a few serotypes (i.e., 1/2a, 1/2b, 1/2c and 4b), which were the same as those found in clinical samples collected during outbreaks and from sporadic cases of listeriosis reported in Italy in the period considered. The geographical distribution of the strains of L. monocytogenes isolated from food samples is very similar to that of the clinical strains.