The data in this package include coral colony size and condition data collected as part of the Guam Long-term Coral Reef Monitoring Program (GLTMP). The monitoring team assesses all coral colonies found within quadrats placed every five meters along 25 m transects (although note that transects of different lengths have been used). Quadrat size is 0.25 sq m for most sites; a larger quadrat size (0.75 sq m) is used for the Western Shoals and Fouha Bay sites. Collected data include measurements of coral colony length and width as well as an assessment of condition (percent old mortality, percent new mortality, disease/condition type and severity), with identification to species level when possible. These data were collected using a split-panel sampling approach, whereby a mix of permanent and non-permanent sampling stations (one sampling station = one transect) are visited within each site. The location of coral colony survey quadrats at permanent sampling stations are marked using masonry nails, facilitating the near-identical positioning of quadrats during subsequent visits. However, the identical re-positioning of some quadrats could not be attained during subsequent visits due to the failure to re-locate the nails. The monitoring sites represent high priority reef areas selected by an advisory body comprised of reef managers, researchers, and technicians. The sites were not selected randomly from around the island and thus should not be considered representative of reef condition at the island-scale. While the general location of the sites were selected based on management priority, the site boundaries were delineated using bathymetry and benthic habitat data within ArcGIS; the locations of the sampling stations were generated randomly within each site’s boundaries using ArcGIS.