The Hatinh langur, Trachypithecus laotum hatinhensis (Dao, 1970), is one of the many Vietnamese primates on the brink of extinction due to hunting and the loss of its natural habitat. This black langur, distinguished by its white moustache and sideburns that extend behind the ears to the nape, inhabits the limestone forests of the Central Annamite Mountains. The Hatinh langur is diurnal and largely arboreal, and group sizes are 15 or more. Here we report on surveys carried out in 1998–1999 in Quang Binh Province to determine the population status of T. laotum hatinhensis. In Vietnam, it occurs only in the limestone areas of five districts in the Quang Binh Province and Huong Hoa District of Quang Tri Province. The most important population is in the Phong Nha–Ke Bang National Park of Quang Binh Province; the only Vietnamese protected area where it is known to occur. Some observations on the species ecology and behavior are also included.