Aims: Salmonella Typhimurium DT 104 is generally assumed to be spread by contact between live animals, e.g. by trading. The aim of the present study was to assess the importance of other routes of transmission in the dissemination of this bacterium. Methods and Results: An outbreak among 14 cattle and pig herds located in a geographically narrow area in Denmark was investigated. Epidemiological information and disease history of the herds was obtained through interviews. Based on this, the hypothesis for horizontal spread was proposed, and these were confirmed by comparison of the pulsed field gel electrophoresis (PFGE) and the plasmid profiles of isolates obtained by continuous sampling over a period of almost 3 years. Conclusions: The study indicated that other routes might play an important role, than the trading of live animals, in the spread of S. Typhimurium DT 104 among livestock. Significance and Impact of the Study: Salmonella Typhimurium DT 104 infected herd might pose a significant risk to herds located within the same geographic area. In advising on how to avoid the spread of this bacterium, factors like person contacts, sharing of equipment and contaminated slurry should be focussed on in addition to infected animals.