Pongo hooijeri is only known from isolatedteeth. In its initial description, it was distinguished from other orangutan species by its generally larger tooth size than living orangutans, as well as a number of morphological characters of the teeth, differing from Pongo pygmaeus "in lacking significant crenelation on the occlusal surfaces of the molars and upper premolars, and on the basins of the lower premolars. Incisors are not known. Molar cusp disposition similar to that of P. pygmaeus, but the cusps themselves are puffier and more rounded occlusally as well as on their external slopes. The occlusal surfaces are thus more poorly defined, and the occlusal basins are more constricted."