El Salvador has the smallest protected areas system in Central America. High levels of habitat destruction and disturbance throughout the country make the reserve system especially important for conservation of biodiversity. I used complementarity approaches to assess the relative conservation importance of ten reserves in El Salvador. The principal criterion was presence of nationally threatened and endangered bird species. Additional criteria included residency status (resident species were more important than migratory non-breeding species) and regionally endemic species. Montecristo National Park was the most important area, with 42% of all nationally threatened birds present. El Imposible National Park, El Salvador's largest park (5000 ha), scored second, followed by Laguna El Jocotal wildlife refuge and Barra de Santiago wildlife refuge. In all, these four areas provide refuge for 83% of El Salvador's 268 nationally threatened bird species in less than 7600 ha of natural habitat. Because of small reserve sizes, all of El Salvador's threatened birds may need additional protection.