Two persons were hospitalized in Spokane, Washington, with infections proved to be caused by Vibrio mimicus. Vibrio mimicus had previously been recognized a cause of gastroenteritis transmitted by various seafood, particularly shellfish. Both persons had eaten boiled crayfish that had been served out of a cooler used to store uncooked crayfish. The cooler had not been sanitized between uses. Some crayfish were leftover from the party and were eaten the next day. Eating the leftover crayfish increased the risk of illness. Two additional cases were discovered during the investigation.