The characterization of Haemophilus parasuis strains is very important for the study of the epidemiology of this agent within and between herds. In the present study, the characterization of H. parasuis field isolates by serotyping and genotyping was compared, and the molecular epidemiology of this agent in North American herds was studied. Results showed that genotyping provided a more accurate characterization of H. parasuis isolates, allowing the comparison of any isolate regardless of its serovar. Serotyping proved to be a limited technique for epidemiological studies on H. parasuis infections. A high genetic diversity was observed within serovars groups. It was observed that affected herds had 1 to 3 prevalent strains of H. parasuis, and that although many herds were affected by the same serovar group, each herd had different prevalent strains. It was also demonstrated that herds receiving the same source of animals shared similar prevalent strains. The epidemiological data presented in this studied can be further used for the development of control strategies to reduce mortality in swine herds due to H. parasuis infections.