Monterey pine (Pinus radiata D. Don) is native to California and widely planted in Mediterranean climates around the world. Pitch canker, a disease caused by Fusarium circinatum Nirenberg and O’Donnell, is a serious threat to P. radiata in native forests and in plantations. Because of its economic importance worldwide, conservation of P. radiata native populations is a high priority. We developed a demographic matrix projection model to simulate dynamics of naturally occurring P. radiata populations in California in the presence of the disease. Tree demography data for the model were collected from seven sites in a native forest on the Monterey Peninsula. Height and stem diameter were recorded for all trees, which were divided into five size classes based on these data. Transition probabilities were calculated for each size class; cone production, seed release, and seed transition probability were estimated using an iterative search process. In the model, pitch canker influences state-specific fecundity and survival probabilities. Five different approaches to include these effects were compared. Populations were projected over 50 decades from three specified initial population sizes. Elasticity analysis indicated that facilitating survival of all size classes is vital to maintaining the structure of the forest.