New records in Tanzania of the Vulnerable Jackson's mongoose Bdeogale jacksoni expand its distribution by over 900 km to the south. During two independent camera-trap surveys over 3 years B. jacksoni, one of Africa's most cryptic small carnivores and previously thought to be endemic to Kenya, was recorded in forests of the Udzungwa Mountains. All records were highly localized within Matundu forest, at a maximum of 2.65 km apart. Most of the records (73%) were between 19.00 and 00.00, confirming that the species is primarily nocturnal. Conservation recommendations include further ecological research, genetic analyses, surveys in other Eastern Arc and ground-water dependent forests, and greater protection for Matundu.