Gough Island, a remote island in the South Atlantic, is home to one of the most important seabird colonies in the world, including 22 breeding species. House mice were introduced to Gough in the 1800s and have since been observed eating seabird chicks and eggs. However, the extent of their impacts on breeding seabird populations was unknown. In this paper we calculated the breeding success of 10 species on Gough and compared these to the breeding success of similar species on islands where there aren't any invasive mammals. We estimated that house mice are responsible for the loss of nearly 2,000,000 chicks and eggs on Gough Island, annually. Some species are more vulnerable than others but almost all were impacted. At least three species that are found nowhere else in the world, the Tristan Albatross, Atlantic Petrel, and MacGillivray's Prion are likely to become extinct in the near future if mice aren't removed from Gough.