Natural hazards and disasters have been common occurrences throughout American history. In the US, natural hazards accounted for more than $300 billion in damages, 9000 fatalities, and over 73 000 injuries in 1975–1998 (Cutter 2001). Annual losses averaged more than $12.5 billion during this same time period. Fortunately, fatalities and injuries have decreased in recent decades (Platt 1999), but crop and property damages from all hazards continue to escalate (Changnon & Changnon 1999, Mileti 1999). In the past 20 yr, for example, there were 46 different billiondollar weather disasters in the US, with a total estimated loss of $277 billion. The majority of these occurred in the 1990s, resulting in $145 billion in losses for the decade alone (National Climatic Data Center, NCDC, 2002). If billion-dollar earthquake events in the last 20 yr also are included (e.g. Loma Prieta and Northridge, CA), another $8 billion can be added to the total. There is no doubt that in the future natural hazards will cause even more destruction of property, as population densities and property values rise, and hazard mitigation policies remain static, especially in many high-risk areas. Among the different natural hazards, flooding caused the most fatalities and the largest losses during the past 25 yr (Cutter 2001). In comparison to other hazard events during this same time period, tornadoes caused the third highest number of fatalities, after floods and lightning. Based on damage totals, tornadoes also ranked third in total dollar losses, right behind floods and hurricanes. This paper examines the spatial and temporal changes in the tornado hazard within the US in order to discover shifts in the relative level of hazardousness