The northern buffed-cheeked gibbon resembles Nomascus gabriellae in appearance. Males and females of N. annamensis differ in morphology and color. The male has a primarily black pelt that glistens silver in sunlight, with a lighter brown chest. The cheeks are a deep golden-orange, and the crest is very prominent. The female, though, lacks the characteristic crest and is orange-beige in color.
The holotype is located in the Zoological Museum of the Vietnam National University.