Species distribution maps are widely used in predicting areas of conservation concern, particularly where species distributions are poorly known. However, the accuracy of range maps for regional/local planning is questionable. We compared published putative geographic range polygons of ten primate species to their actual occupancy at 23 survey sites in southeastern Peru to assess the fine-scale accuracy of these polygons for regional conservation planning. We analyzed the proportion of sites at which each species was detected, both inside and outside of its published NatureServe [Patterson et al., Digital distribution maps of the mammals of the western hemisphere. Version 1.0. Arlington, VA, 2003] and IUCN [2008; Red List, 2008] range polygons. There were mismatches between our line-transect survey data and range polygon boundaries for nine of the ten species (from 15 to 80% cases), including both false presences and false absences. Each published dataset overestimated the presence of seven primate species and the absence of four species, though errors varied among species. Occupancy patterns of species with larger geographic ranges were no more accurately predicted than those of more narrow-range species. Regional barriers to dispersal, such as rivers, and finer-scale ecological specialization may limit the applicability of range map polygons to regional-scale conservation priority setting, even for relatively well-studied taxa. Despite the risk of errors, range polygons are still used as baseline data in conservation planning. We suggest some measures that could reduce the error risk.