Dendrolagus scottae n.sp. inhabits mossy forest above 1,200 m on the North Coast Range, Papua New Guinea. Its total known habitat area is estimated at about 25-40 km2. The species is gravely endangered, and its plight is symptomatic of that of many large mammals in Melanesia. Dendrolagus scottae differs from all other tree-kangaroos in its uniform blackish colouration, narrow but long dentary, shallow face, and wide P/3 with a large posterobuccal cusp. The combination of large cheekteeth but small masticatory muscles suggest that D. scottae n.sp. has a different feeding strategy to other tree-kangaroos. Dendrolagus scottae n.sp. and D. dorianus possess a number of features which are unique among near relatives. These include the presence of a greatly reduced superior lachrymal foramen, large cheekteeth, uniformly dark dorsal and ventral colouration, and a very short tail. These derived features indicate that these two species are each other's closest relatives.