The foodborne pathogen Listeria monocytogenes is able to survive for months and even years in food production environments. Among a great strain diversity particularly strains belonging to sequence type (ST)121 are able to persistent in food production plants. To elucidate the molecular determinants specific for L. monocytogenes ST121, we determined the genomes of 14 ST121 strains, and compared them with all available L. monocytogenes ST121 genomes.