Mountain pine beetle (MPB) (Dendroctonus ponderosae Hopkins) is a native bark beetle that reproduces in pine (Pinus) species across western North America. High population levels can result in widespread host tree mortality. Over the past 2 decades, MPB has been responsible for pine mortality across millions of forested hectares in the western United States. Although a majority of the pine species found in the western United States are considered hosts to MPB, the host status of Rocky Mountain (RM) bristlecone pine (Pinus aristata) is unclear. We surveyed stands across the range of RM bristlecone pine in Colorado, USA, and quantified MPB-caused mortality within the past 10 years in stands where RM bristlecone and at least one other pine species co-occurred. We also evaluated in the field whether successful MPB brood production occurred in RM bristlecone pine. Our results confirm that RM bristlecone pine is susceptible to MPB attack and suitable for MPB reproduction. In mixed-species stands, pine species availability influenced MPB attack occurrence. The proportion of trees experiencing fatal beetle attack within a particular Pinus species was best predicted by the basal area proportion of that species in the stand prior to the most recent 10 years of mortality. These results indicate that RM bristlecone pine is vulnerable to ongoing climate change–induced contact with MPB.