The distribution and ecology of Assamese macaque Macaca assamensis remains little studied in South-east Asia. This review collates historical and recent records to clarify its range and habitat use in Lao PDR. Contrary to many standard sources limiting Assamese macaque's range to the north and center of the country, it occurs well into the southern part. In the country's three physiographic units, it is widespread in the northern highlands and the Annamite range, but seems absent from the Mekong plain. Most records are from hill evergreen forest above 500 m, consistent with standard literature, but the species occurs down to plains level (200 m) on karsts (at least in areas south of 16°58′N). The few records from below 500 m off karst are all in ragged terrain, but even so non-karst ragged land below 500 m seems to be only rarely used. Ecological overlap with northern pig-tailed macaque M. leonina and with Rhesus macaque M. mulatta is very limited in Lao PDR. In the long-term, hunting and forest encroachment may threaten Assamese macaque in Lao PDR, but it is much less imminently at risk in the country than are most gibbon and colobine species.