The author of the last published systematic review of Cacajao recognized 2 subspecies of black-headed uakaris (black uakaris): Cacajao melanocephalus melanocephalus and C. m. ouakary. As a result of a series of black uakari surveys and collecting expeditions to several tributaries of the Rio Negro and of morphological and molecular analyses of museum specimens and specimens we collected during field expeditions, we reassess their taxonomy. We describe a newly discovered species of black uakari from the Rio Aracá, a left bank tributary of the Rio Negro, Amazonas, Brazil. We also show that ouakary is a junior synonym of melanocephalus and provide a new name and a new description for Cacajao melanocephalus melanocephalus in the Pico da Neblina region of Brazil and Venezuela. Based on genetic, morphological, and ecological evidence, we propose that there are 3 species of black uakaris. We named the Rio Aracá species Cacajao ayresi sp. nov. (Ayres uakari) in honor of the late José Márcio Ayres, a pioneer in uakari research and conservation. We named the Neblina black uakari Cacajao hosomi, after the Yanomami word for uakaris. The new taxonomic arrangement provided here implies that the conservation status of black uakaris needs to be reassessed.