The etiologic agents and food vehicles associated with the 7458 outbreaks (involving 237,545 cases) of foodborne disease reported to the Centers for Disease Control between 1973 and 1987 were examined. Bacterial pathogens accounted for 66% of outbreaks and 87% of cases, viruses 5 and 9%, parasites 5 and <1%, and chemicals 25 and 4%, respectively. Salmonella accounted for 42% of outbreaks and 51% of cases due to bacterial pathogens. When data from 1973–75 were compared with 1985–87, a 75% increase in the proportion of outbreaks and 130% increase in the proportion of cases due to Salmonella were observed; in particular, outbreaks due to Salmonella enteritidis increased markedly. The proportion of Salmonella outbreaks with a known vehicle that were associated with beef (the food most frequently associated with Salmonella outbreaks) peaked at 30% in 1981, dropped to 4% in 1982, and has since risen gradually. The proportion of Salmonella outbreaks due to chicken and eggs increased over the study period. Bacteria not previously recognized as important foodborne pathogens that emerged during the study period include Campylobacter jejuni, Escherichia coli 0157:H7, and Listeria monocytogenes. Bacterial pathogens accounted for 90% of deaths, with L. monocytogenes (317/1,000 cases) and Clostridium botulinum (192/1,000 cases) having the highest death-to-case ratios. The proportion of outbreaks in which the food was prepared in a commercial or institutional establishment and the median outbreak size both increased. Investigation and analysis of foodborne disease outbreaks continue to play a key role in understanding foodborne illness and in designing and evaluating control measures.