Stand conditions associated with outbreak populations of the roundheaded pine beetle, Dendroctonus adjunctus Blandford, in ponderosa pine, Pinus ponderosa Dougl. ex Laws., forests were studied in the Pinaleno Mountains, AZ, and the Pine Valley Mountains, UT. Classification tree models to estimate the probability of infestation based on stand attributes were built for both study areas using growth rate and ponderosa pine basal area information. Cross-validation estimates of correct classification were 0.60 for the Pinaleno Mountains and 0.58 and 0.78 for the Pine Valley Mountains. Regression tree and linear regression models to estimate amount of mortality caused by the beetles were also built for both sites using growth rate, ponderosa pine basal area, and trees per hectare information. The occurrence and mortality levels caused by the roundheaded pine beetle are positively related at both the stand and tree scale with reduced growth rates caused by high stocking densities.