Factors that contributed to foodborne outbreaks that were reported in the U.S. from 1973-1976 are identified and categorized by disease and by locale in which incriminated foods were mishandled. Data from the same years are tallied separately and combined with data from the years 1961-1972. Inadequate cooling was associated with most foodborne outbreaks, with many bacterial foodborne diseases (such as salmonellosis, staphylococcal food poisoning, and Clostridium perfringens gastroenteritis), and frequently with outbreaks that originated from foods prepared in foodservice establishments and homes. Inadequate cooling practices were usually either failure to refrigerate cooked foods or the storing of foods in large stock pots or other large containers that were refrigerated. Other important factors that contributed to foodborne outbreaks were the lapse of a day or more between preparing and serving (coupled with inadequate refrigeration or hot-holding during this time), handling of cooked foods by infected persons, inadequate cooking or other thermal processing, inadequately high temperatures during hot storage, inadequately high reheating temperatures, inadequate cleaning of kitchen or processing equipment, ingestion of contaminated raw food or ingredient, and cross contamination. The frequency of involvements of the factors that contributed to outbreaks in England and Wales was quite similar. The principal factors that contributed to staphylococcal food poisoning were inadequate cooling practices, infected person manipulating cooked food, and lapse of a day or more between preparing and serving. The principal factors that contributed to C. perfringens gastroenteritis were inadequate cooling practices, lapse of a day or more between preparing and serving, and inadequately high temperatures during hot-holding and reheating. The principal factors that contributed to salmonellosis were inadequate cooling practices, contaminated raw ingredients, inadequate cooking or thermal processing, and cross-contamination.