Lichens are the dominant organisms on most of the South Atlantic island of St Helena. In total, 220 different species were found during a recent survey, most of which have never been reported from the island. Previously, less than 50 lichen species were reported from the island, one half of which are most probably incorrect records. The total number of lichens known from the island now stands at 225. Most species could be identified, but the following, most probably endemic, species are described as new to science: Dolichocarpus seawardii, which is only the second species in this genus, the type being from Chile; Dermatiscum pusillum, which is only the third species in this African genus; Dimelaena triseptata; Xanthoparmelia beccae; and four Ramalina species, Ramalina geniculatella, R. ketner-oostrae, R. rigidella, and R. sanctae-helenae. The lichen flora has many species in common with that of the geologically much younger Ascension Island, where just under 100 species were recently found by the author, most of which are equally new to that island. Lecanora sanctae-helenae, previously known as the only endemic lichen of St Helena, was also found to be abundant on Ascension Island. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158, 147–171.