Lao Peoples' Democratic Republic (i.e., Laos), situated in the center of the Indochina Peninsula and encompassing 14–22.5°N, consists of diverse environments, including Xay Phou Louang (Annamite Cordirella) in the east, the Mekong River in the west, and plains in between. More than 15 percent of the national land area has been designated as National Protected Areas (NPAs) by the government of Laos since 1993. Compiling museum data and literature, Fooden (1980, 1995) sketched the distribution of long-tailed macaques in Laos. In addition, assessments were carried out in the 1990 on Laos's wildlife in these NPAs and these surveys also reported the distribution of macaques (Duckworth et al., 1999). These reports suggested that long-tailed macaques were distributed only in southern-most Laos, which is a region consisting of mountainous areas (i.e., Bolaven plateau, Xay Phou Louang) and tributaries of the Mekong River. However, the present distribution and current population status of long-tailed macaques are not known.
Primate fauna is rich in southern-most Laos, which includes prosimians (i.e., lorises), cercopithecids, colobines, and lesser apes (i.e., gibbons) (Duckworth et al., 1999). Laos contains highly endangered species, such as red-shanked douc langurs (Pygathrix nemaeus) and yellow-cheeked gibbons (Nomascus leucogenys gabriellae; Duckworth et al., 1999), as well as typically common monkeys such as the rhesus (Macaca mulatta) and long-tailed macaque (M. fascicularis). All non-human primates in Laos are currently under threat of extinction because their habitats have been lost to commercial logging, hydraulic power development, and agriculture, all of which have been driven by increases in human population, economical development dependent on natural resources, and foreign capital (Duckworth et al., 1999).