In 1986-87 the Centers for Disease Control conducted an active population-based survey of Listeria monocytogenes infections in six regions of the United States. Listeriosis was reported in 154 patients: one-third of cases were perinatal and the remaining two-thirds occurred in the elderly and immunosuppressed. 28% of cases were fatal. 82 cases and 239 controls matched for age and underlying disease were enrolled in a study of risk factors for listeriosis. Cases were significantly more likely than controls to have eaten uncooked hot dogs or undercooked chicken, with 20% of the overall risk of listeriosis attributable to consumption of these foods. No other risk factors were identified.