Whitebark pine (Pinus albicaulis), an important producer of food for wildlife, is decreasing in abundance in western Montana due to attacks by the white pine blister rust fungus (Cronartium ribicola), epidemics of mountain pine beetle (Dendroctonus ponderosae) and successional replacement mainly by subalpine fir (Abies lasiocarpa). Plots established in 1971 were remeasured in 1991 and 1992 to determine the rate and causes of whitebark pine mortality. Mortality rates averaged 42% over the last 20 yr. indicating a rapid decline in whitebark pine populations of western Montana. This decline is most pronounced in northwestern Montana with the southward extension of heaviest mortality centered along the continental divide and Bitterroot Mountain range. Management treatments such as prescribed fire can serve to maintain whitebark pine in the landscape.