Residents in the southeastern United States would hardly describe life with the aggressive imported fire ant as peaceful coexistence. The continued spread of these insects has produced agricultural problems, changes in the ecosystem, and increasing numbers of subjects with sting sequelae, including hypersensitivity reactions, secondary infections, and rare neurologic sequelae. Evolutionary changes have facilitated their expansion northward into Virginia and westward into California, and increasing urbanization will likely permit further expansion. Recent reports of building invasion with sting attacks inside occupied dwellings, including health care facilities, heighten public health concerns. This article reviews the medically important entomology, clinical aspects of stings, and the current approaches to chemical control of fire ants. We also propose directions for future research and treatment.(J Allergy Clin Immunol 2000;105:683-91.)