Karyotypic variability in Aotus suggests at least seven species in the gray-necked group (A. brumbacki, A. griseimembra, A. lemurinus, A. trivirgatus, A. vociferans, A. zonalis, and Aotus sp. nov.) based on six known karyomorphs, highly divergent mitochondrial cytochrome c oxidase sequences, different sensitivities to malaria, varied mitogenic and immunological responses to other diseases, and well-defiined geographical distributions, and the likelihood that these species are distinctive enough to possess reproductive barriers. We discuss these karyomorphs and explain why A. brumbacki cannot be an A. lemurinus subspecies. We briefly describe a karyotype for Aotus from Maipures on the Rio Orinoco and suggest that this represents A. brumbacki, extending our knowledge of that species' distribution to the Orinoco basin. We stress the presence of a new undescribed Aotus in Colombia from a completely unknown location, which we name Aotus jorgehernandezi in honor of Jorge I. Hernández-Camacho. We discuss the meaning and evolution of chromosome variability, the nature of Aotus as a sibling species complex and the use of the phylogenetic versus biological species concepts in primatology.