A commercial duck company that raises approximately two million Pekin ducks per year experienced an outbreak of Riemerella anatipestifer (RA) on nine farms over a 1-yr period. Owing to concerns that the bacteria was being spread from farm to farm, an investigation using serotyping and DNA fingerprinting was performed. The results revealed that there were three different strains of RA involved in the outbreak. One strain was spread from one farm to six other farms, while another strain from the same farm was spread to two other farms. These findings add additional proof of the value of DNA fingerprinting in disease outbreak investigations and further support the importance of implementing biosecurity protocols to stop the spread of disease-causing organisms.