Sanje mangabeys (Cercocebus sanjei), first described in 1981, are among the most endangered primates in the world. They are endemic to the Udzungwa Mountains of Tanzania, in a biogeographic region designated one of the world's biodiversity hotspots. Conservation research since 1997 has documented the presence of the mangabey in only 3 of the relict montane forest blocks of the Udzungwas. The total population, possibly < 1,500 animals, is fragmented and not adequately protected. A substantial proportion (perhaps 40%) live in forest reserves outside the protective confines of the Udzungwa Mountains National Park, and they are affected by habitat loss and hunting. Efforts to improve their conservation status include assessment of distribution, relative abundance, and habitat quality, and initiation of observational research with habituated individuals to acquire critically important data on their habitat requirements, diet, movement patterns, socioecology, and community ecology. These interrelated research activities should contribute to effective management for conservation, provide baseline information to support current efforts to expand the boundaries of the national park, and guide potential future establishment of corridors between the major forests known to support mangabey groups.PUBLICATION ABSTRACT