Maintaining an ecosystem shaped primarily by natural geological and ecological processes is a primary goal in Yellowstone National Park (YNP) (Houstori 1971). Thus, one important question about the fires of 1988 is whether they were really natural: Did they behave as they would have if Europeans had never entered the area? The park had a policy of co mplete fire suppression from 1872 to 1972, so past fire control may have led to abnormal fuel conditions and therefore to abnormal fire spread and behavior in 1988 (Dodge 1972, Kilgore and Taylor 1979). In this article, we compare the fires of 1988 with fires during the previous 350 years. We use both information contained in park files and results of our tree-ring research on the prehistoric fire history .