Of the seven species of atelids occurring in Peru, three are present in the northeast of the Amazon; one of them, Ateles belzebuth, is listed as Endangered on the IUCN Red List of Threatened Species. These primates are preferred game, but detailed information on group size, population density and conservation status is scarce. We conducted transect censuses in forests with different levels of human disturbance (low, moderate and high), and also surveyed forests along the northern and southern banks of the Río Marañón. We recorded 232 groups of three species along 2, 126 km of transect censuses. Group size and population densities of Lagothrix lagothricha poeppigii and Alouatta seniculus were lower in forest where human disturbance was ranked as high, compared to forests of low and moderate human disturbance. Ateles belzebuth had been extirpated in the area of high human disturbance. Besides hunting, increasing deforestation is a major threat to the survival of atelids in the northeast of the Peruvian Amazon.