Formerly considered a subspecies of the Banded Surili (Banded Leaf Monkey), the White-thighed Surili is now classified as a species in its own right.

The species is slender in build, with greyish or brownish-grey fur which becomes light grey to whitish on the underside and around the cheeks. Juveniles have distinctive spiked fur on top of the head. The eyes are framed by light fur/skin beneath and a line of pale fur at the side. The tail is dark.

Social groups of the species comprise an adult male, several females, juveniles and young. They feed on young leaf shoots, seeds and forest fruits.

Shown here (top left) is the P. s. siamensis subspecies, which is  common in the extensive sub-montane forests of central Peninsular Malaysia.

Also shown (bottom left) is a rare image of the P. s. rhionis subspecies from Bintan Island, Riau Archipelago, Indonesia.

Other subspecies of the White-thighed Surili occur in the Riau Archipelago and parts of eastern Sumatra.