Abstract: The isolated Mid-Atlantic Ridge islands of Ascension Island (8° S), St Helena (16° S), and Tristan da Cunha (37° S) are 1700 - 2800 km from Africa, the nearest continent. We compiled published, unpublished, and new records of ants from these islands and evaluated the probable origin of each species. We examined specimens representing 20 different ant species: ten from Ascension, 16 from St Helena, and one from Tristan da Cunha. These included three new records from Ascension (Pheidole teneriffana Forel, 1893, Solenopsis sp. 1, Strumigenys emmae (Emery, 1890)), five new records from St Helena (Hypoponera sp. 1, Linepithema humile (Mayr, 1868), Monomorium latinode Mayr, 1872, Monomorium cf. sechellense, Pheidole teneriffana), and the first identification of the only ant species known from Tristan da Cunha (Hypoponera eduardi (Forel, 1894)). All confirmed island records, except Camponotus fabricator (F. Smith, 1858) and Hypoponera punctatissima (Roger, 1859) on St Helena, included specimens from 1995 or later. We could not confirm two additional published ant species records from Ascension (Cataglyphis sp., Tapinoma sp.) and one from St Helena (Camponotus castaneus (Latreille, 1802)). Most, if not all, of the 20 ant species we documented on South Atlantic islands, including C. fabricator, a putative St Helena endemic, may be exotic species that arrived accompanying humans. However, it is possible that some ants were present before human arrival. One candidate for native status is Cardiocondyla mauritanica Forel, 1890, a widespread tramp species originally from Africa, found on Ascension in many uninhabited areas.