As an island endemic, the Island Scrub-Jay's Aphelocoma insularis population status and conservation are of concern. In addition, because the Island Scrub-Jay is easily observed, it is an ideal candidate for monitoring the effects of management efforts on Santa Cruz Island, California. We used estimates of territory size in several different habitats occupied by the Island Scrub-Jay and the total area of these habitats on the island to develop an empirical estimate of the population size for this species. Our most conservative, and we feel most realistic, estimate for the Island Scrub-Jay breeding population is 7,000 individuals and for the non-breeding population 5,500 individuals, yielding a total population estimate of 12,500. Even though conservative, this estimate is larger than earlier estimates of 4,000 to 6,000 individuals. Even so, our data suggest no reason exists for immediate concern regarding the population viability of the Island Scrub-Jay and they provide a baseline for future estimates and comparisons. Most importantly, this population estimate can be used to monitor the influence on the Island Scrub-Jay of future island management efforts, especially regarding exotic tree species and feral pigs.