In July 2004, a cluster of Salmonella Enteritidis isolates were matched using pulsed-field gel electrophoresis (PFGE) technique, a genetic fingerprinting technique. The Arizona State Health Department interviewed the persons associated with these isolates and determined a common exposure source for the cases. Eighteen of the twenty cases had visited Rocky Point, Mexico, in early July and ten of these persons recalled eating a shrimp cocktail during their visit. Eating shrimp was significantly associated with illness. Further investigation into the food was impossible as the source was not within the jurisdiction of the USA.