During the summer of 1999, a heat wave occurred in the midwestern and eastern United States. This period of hot and humid weather persisted from July 12 through August 1, 1999, and caused or contributed to 22 deaths among persons residing in Cincinnati (18 deaths) and Dayton (four deaths). A CDC survey of 24 U.S. metropolitan areas indicated that Ohio recorded some of the highest rates for heat-related deaths during the 1999 heat wave, with Cincinnati reporting 21 per million and Dayton reporting seven per million (CDC, unpublished data, 1999). This report describes four heat-related deaths representative of those that occurred in Cincinnati or Dayton during the 1999 heat wave, summarizes heat-related deaths in the United States during 1979-1997, describes risk factors associated with heat-related illness and death, and recommends preventive measures.