In comparison to other ecosystems in east Africa, the biodiversity of the coastal forests of Kenya's northern coastline is poorly documented, even in the case of large terrestrial mammals. In response to this, we undertook a systematic survey of the Boni-Dodori forests using four camera trap grids with camera spacing of 2 km covering 300 km² over 7020 camera trap days. We recorded 37 mammal species and derived camera trap rates and estimated occupancy for 31 medium-to-large terrestrial species, some of which represent range extensions. Remarkably, the critically endangered Aders' duiker was the most frequently recorded species. A distinctive form of giant sengi and the vulnerable Sokoke bushy-tailed mongoose were also widely distributed and relatively abundant. Other significant records of threatened species included African wild dog, African lion and Pousargues's monkey. Species richness and relative abundance of all species were higher than that recorded for Arabuko-Sokoke Forest, Kenya's only other large coastal forest, using the same camera trap survey protocol.