Edema disease is a systemic disease of weaned pigs caused by host-adapted strains of Escherichia coli, most commonly belonging to serogroup O138, O139, or O141. In the late 1990s, E. coli O147 strains containing the virulence genes f18,sta, stb, and stx2 were recovered from outbreaks of edema disease in the United States. Pulsed-field gel electrophoresis (PFGE) was used to determine that the majority of these strains (34/43) were closely related to one another. Subsequent analysis by multilocus restriction typing confirmed the PFGE results and indicated that the cluster of edema disease strains were only distantly related to other E. coliO147 strains. Serogrouping of edema disease isolates from the Iowa State University Veterinary Diagnostic laboratory recovered between 1996 and 2000 indicated that 42% belonged to serogroup O147. Our data suggest that these strains may be a common serotype of edema disease-causing E. coli in the United States.