Shiga toxin-producing E. coli (STEC) O157 is a significant cause of foodborne illness in the United States. ERS estimated the economic cost of illness due to this pathogen— $405.2 million (in 2003 dollars)—using the most recent estimate (1997) of the annual number of STEC O157 cases by the Centers for Disease Control and Prevention (CDC) and medical and cost data from the Foodborne Diseases Active Surveillance Network. CDC is currently updating its estimate of annual cases. As new information becomes available, the ERS online Foodborne Illness Cost Calculator enables users to review and modify the assumptions underlying the STEC O157 cost estimate, such as the number of cases, and then recalculate the cost, adjusted for inflation for any year from 1997 to 2006. The potential utility of the calculator was demonstrated by assuming that the incidence of STEC O157 had declined and then estimating the cost for a smaller number of cases.