Hypothermia results from the inability of the body to maintain a sufficiently high body temperature and is defined clinically as the lowering of core body temperature to < or = 95 F (< or = 35 C). Environmental hypothermia results from a combination of heat loss by convection (degree of wind exposure), conduction, and radiation to the surrounding air. Although hypothermia-related deaths are preventable, during 1979-1990, 9362 deaths in the United States were attributed to environmental hypothermia or excessive cold (International Classification of Diseases, Ninth Revision [ICD-9], codes E901.0, E901.8, and E901.9; excludes manmade cold [E901.1]). From November 1992 through March 1993, 22 hypothermia-related deaths were identified by the Cook County (Chicago), Illinois (1990 population: 5,105,067), medical examiner. This report summarizes information on those deaths and describes specific findings in four of the deaths.