Food-borne zoonoses have a major health impact in industrial countries. Campylobacter spp., Salmonella enterica, Yersinia enterocolitica and Listeria monocytogenes are high-risk food-borne zoonotic hazards in finishing pigs. The objectives of this work were (1) to study the isolation rate of pathogenic Y. enterocolitica, Salmonella spp., Campylobacter spp. and L. monocytogenes in the tonsils and feces and (2) to determine the number of mesophilic aerobic bacteria (MAB) and Escherichia coli in the tonsils of fattening pigs at slaughter. The samples, which were collected from one slaughterhouse on five occasions, originated from 50 pigs and 15 farms. The number of MAB varied from 6.40 to 7.82 log(10) CFU/g and E. coli from 4.38 to 6.53 log(10) CFU/g. Additionally, 31 (62%) of the tonsils were colonized with Y. enterocolitica and 16 (32%) with L. monocytogenes. Campylobacter spp. were more frequently excreted in feces and only 3 (6%) of the pigs carried Campylobacter spp. in the tonsils. No Salmonella spp. were isolated. The pig tonsils were shown to be colonized with a high number of bacteria including E. coli, which is the most important indicator for fecal contamination, and with Y. enterocolitica and L. monocytogenes, which are important food-borne pathogens. This study demonstrates that the tonsils are highly contaminated with micro-organisms and can be a very important source of contamination in the slaughterhouse.