Like other closely related lutungs, Delacour's langur has a crest of long, upright, hair over the forehead and crown; this is, however, somewhat taller and narrower than in other species.

The largest surviving population is thought to live in Van Long Nature Reserve in Ninh Bình, where the it inhabits open forest up to elevations of 328 m (1,076 ft) in terrain dominated by limestone karst.

[5] The monkeys have been reported to eat leaves from a wide range of different plant species, indicating that their apparent dependence on limestone habitats is not related to their diet.

When potential rivals are spotted, the males in a troop initially try to intimidate them with loud hoots and visual displays, resorting to chasing and fighting if this fails.

They swing by their hands when travelling through trees, and use their tails for balance when scrambling over steep rocky terrain, which may allow them to move more rapidly than other related lutungs.

[3] Classified as critically endangered by the IUCN, the primary threat to the species is hunting for traditional medicine, with loss of forest habitat and the local development of tourism also being a potential risk.