Background. Osteoprotegerin (OPG), an immunoregulatory member of the TNF receptor superfamily, is expressed in inflamed intestinal mucosa. We investigated whether OPG is produced by intestinal epithelial cells and tested the hypothesis that single-nucleotide polymorphisms (SNPs) in the gene encoding OPG (TNFRSF11B) are associated with traveler's diarrhea (TD) among North American travelers to Mexico. Methods. OPG concentration was measured in the supernatants of T84 cells infected with various diarrheagenic Escherichia coli pathotypes. Genotyping was performed for 4 SNPs in the OPG gene for 968 North American travelers with or without TD. Stool samples from travelers with TD were evaluated for the presence of enteric pathogens. Results. T84 cells produced higher OPG levels in response to infection with various diarrheagenic E. coli pathotypes than with E. coli controls (P < .05). A SNP in the exon 1 region of the OPG gene (OPG +1181G>C) was associated with TD in white travelers who stayed in Mexico for >1 week during the summer (P = .009) and for TD due to nonsecretory pathogens (P = .001). Conclusions. Our study suggests that OPG is secreted by intestinal epithelial cells in response to enteropathogens and that a polymorphism in the OPG gene is associated with an increased susceptibility to TD. © 2009 by the Infectious Diseases Society of America. All rights reserved.