The cetacean fauna at the Tristan da Cunha archipelago has been assessed from ship-based, aerial and land-based observations from 1983–2000, from strandings on Tristan da Cunha and Inaccessible Island between 1983 and 1995, and from whaling catch data from 1934–1967. Five species (Eubalaena australis, Megaptera novaeangliae, Tasmacetus shepherdi, Globicephala melas and Orcinus orca) have been sighted within the territorial waters of the archipelago, eight species (Balaenoptera physalus, B. borealis, B. acutorostrata/bonaerensis, Physeter macrocephalus, Mesoplodon mirus, M. bowdoini, Delphinus sp. and Lissodelphis peronii) have been seen or taken within 200 nautical miles (360 km) of the group or have been found stranded on its shores, while another two species (Caperea marginata and Lagenorhynchus obscurus) have been recorded close enough to be considered likely to occur within 200 nautical miles. The records of Mesoplodon mirus and M. bowdoini represent significant extensions to their known distribution. Apart from its possible importance as a mid-oceanic nursery area for southern right whales, the waters of the Tristan Archipelago seem to be a concentration area for T. shepherdi, one of the least-known of the world's cetaceans.