Estimates of the magnitude of foodborne illness in the United States have been imprecise. To quantify, better understand, and more precisely monitor foodborne illness, since 1996 the Foodborne Diseases Active Surveillance Network (FoodNet) has collected data to monitor nine foodborne diseases in selected U.S. sites. This report describes preliminary data from FoodNet surveillance for 1998 and compares findings with those for 1996 and 1997; compared with 1996, the overall incidence of the foodborne illnesses under surveillance during 1998 declined, particularly for salmonellosis and campylobacteriosis, and the data continued to demonstrate regional and seasonal differences in the reported incidence of diseases.