Factors that contributed to outbreaks of foodborne diseases reported in the U.S. from 1977–1982 are identified and classified by disease and place where implicated foods were mishandled. Data for these years are tabulated and combined with data from the years 1961–1976. Inadequate cooling - either leaving foods at room or warm outside temperatures or storing them in large containers while being refrigerated - was associated with most of the outbreaks. Ranking of all factors has changed little over four periods of review, but during the last period numerous outbreaks primarily due to ingestion of raw clams and raw oysters caused an increase in the factors: contaminated raw foods and obtaining foods from unsafe sources. This has been primarily due to raw clam-, oyster- and milk-associated outbreaks. The three most frequently identified factors that contributed to salmonellosis were improper cooling, contaminated raw products, and inadequate heating; to staphylococcal food poisoning were colonized persons handling cooked foods, lapse of 12 or more hours between preparing and eating, and improper cooling; to botulism were inadequate heat processing, improper fermentations, improper room temperature holding; to C. perfringens enteritis were improper cooling, lapse of 12 or more hours between preparing and eating, and inadequate reheating (followed closely by improper hot holding); to shigellosis were colonized persons handling implicated foods, improper cooling, and lapse of 12 or more hours between preparing and eating; to V. parahaemolyticus gastroenteritis were contaminated raw ingredients, improper cooling, and cross contamination; to typhoid fever were colonized persons handling implicated foods, lapse of 12 or more hours between preparing and eating, and several time-temperature factors tied for third; to B. cereus gastroenteritis were improper cooling, lapse of 12 or more hours between preparing and eating, and improper hot holding. The principal factors associated with outbreaks stemming from foods prepared in foodservice establishments were improper cooling, lapse of 12 or more hours between preparing and eating, colonized persons handling implicated foods, inadequate reheating and improper hot holding. Important factors that contributed to outbreaks in homes were contaminated raw foods, inadequate cooking, unsafe source, improper cooling, and lapse of 12 or more hours between preparing and eating. Major contributing factors associated with operations in food processing plants were inadequate heat processing, contaminated raw ingredient, improper cooling, colonized persons handling implicated foods, improper cleaning of equipment, and improper fermentation. Those factors cited above for each category are the vital few items to stress in food safety programs. The many other items that are a part of food protection programs are of lesser importance or trivial.