The black-mantled tamarin, Saguinus nigricollis, is a species of tamarin from the northwestern Amazon in far western Brazil, southeastern Colombia and northeastern Peru. It has often included the Graells's tamarin as a subspecies (in which case the distribution extends into eastern Ecuador), but differs from that species in having reddish-orange rump and thighs. The two are often said to be sympatric in Colombia (a major argument for treating them as separate species), though the accuracy of such reports has been questioned. The body length is 15–28 cm. The tail length is 27–42 cm.