The mountain pine beetle, Dendroctonus ponderosae Hopkins, is a significant agent of tree mortality in lodgepole pine (Pinus contorta Dougl. ex Loud.) forests throughout western North America. A large outbreak of mountain pine beetle caused extensive tree mortality in north-central Colorado beginning in the late 1990s. We use data from a network of plots established in 2006-2007 on the Sulphur Ranger District of the Arapaho and Roosevelt National Forests to develop simple probability of infestation and extent of mortality models using classification and regression trees, respectively. A classification tree indicated that when live lodgepole pine basal area was equal to or greater than 59.3 ft2/acre pre-outbreak, the probability of infestation increased. A second classification tree added lodgepole pine mean diameter as a second splitting variable. The rate of correct classification for both models was greater than 0.79. Two regression trees also used live pre-outbreak lodgepole pine basal area as a splitting variable and indicated increasing basal area killed with increasing live lodgepole pine basal area. These simple models use readily available data from forest inventories and can be used to identify stands, based on forest stand conditions, where mountain pine beetle is more likely to occur and the potential extent of lodgepole pine tree mortality should an outbreak occur.