The red leaf monkey, or maroon surili, inhabits primary and secondary forest on the island of Borneo, up to elevations of around 2000 metres. It appears to adapt reasonably well to areas of regenerating, logged forest.

Like other leaf monkeys, this species feeds on a variety of fresh leaves, seeds, fruits and flowers.
Davis & Baillie (1988) described how some populations of the species specialize in eating mainly large, dry forest seeds, devoid of flesh, and only revert to a diet of young leaves, flowers and fleshy fruits at such times that large seeds are unavailable.

Consumption of earth from arboreal termite mounds has also been observed, which may be an attempt to reduce stomach acidity or to increase mineral intake.

The species has reddish-maroon fur throughout its body and tail, with some variation between different populations and subspecies. Its facial skin is grey to bluish-grey, and its lower lips are pale. Infants are creamy to buff.

A number of subspecies are recognized based on different criteria. Two of the subspecies are well defined, namely the 'orange-naped red surili' Presbytis rubicunda ignita (from Sarawak and Brunei) and the 'orange-backed red surili' Presbytis rubicunda chrysea (from eastern Sabah), but further work is required to define other subspecies.

Typically different populations and races may be separated by large, lowland rivers. This implies that in upland areas, where rivers are narrow and are more easily crossed, the distinction between different subspecies may not be so clear.

The red leaf monkey is widespread throughout much of Borneo, occurring in Sarawak and Sabah (Malaysian Borneo), Kalimantan and nearby islands (Indonesian Borneo), and Brunei.