The hill forests of Karen State, Myanmar, were previously inaccessible to biologists and conservationists for security and political reasons. We have, however, now been able to conduct six surveys across the area, using camera traps, for a total of 9,511 trap-nights, to ascertain the presence of threatened mammal species. We obtained 4,191 records of at least 31 mammal species, including 17 categorized as Near Threatened, Vulnerable or Endangered on the IUCN Red List. Carnivores were especially diverse, with 19 species recorded, indicating a globally significant community, including the tiger Panthera tigris, leopard Panthera pardus and dhole Cuon alpinus. Our methodology was not appropriate for estimating relative abundance or occupancy but the species richness of the mammal community, the number of records and the number of locations where species were detected suggest the area is important for the conservation of a globally threatened mammal community that is in decline across the majority of its range. Despite long-standing conservation efforts undertaken by the Karen people, their forests are threatened by hunting and habitat loss. These threats are likely to be exacerbated as political change brings rapid development. Urgent action is thus needed to assist the Karen people to protect one of South-east Asia's last intact rich and diverse ecosystems.