The white-fronted spider monkey, Ateles belzebuth, is listed as 'Endangered' according to the IUCN classification. In Peru it is found in the departments of Loreto, San Martín, Amazonas and Cajamarca, but detailed data on its geographic distribution, population densities and conservation status are scarce. In order to obtain such information, we conducted transect censuses on the Río Aushiri and Río San Antonio (right bank of Río Napo), and between the Río Curaray and the Río Arabela and Río Nashiño, respectively, and made additional explorations on the northern and southern banks of the Río Marañón. We obtained 48 sightings along 761 km of census transect. Group size and population densities were lower in an area with high hunting pressure compared to areas with medium or low hunting pressure. Besides hunting, increasing deforestation is a major threat to the survival of A. belzebuth in Peruvian Amazonia.