The locomotor and postural behavior of Ateles geoffroyi and Ateles paniscus was studied in Panama and Surinam. Ateles locomotion can be divided into five patterns on the basis of limb usage: quadrupedal walking and running, suspensory locomotion, climbing, bipedalism and leaping. The first three are commonly used in both locomotion during travel and locomotion during feeding, but climbing (especially 'horizontal climbing') is the most important pattern during feeding. Most Ateles locomotion takes place on twigs and branches, with twigs playing a greater role in feeding than in travel. Feeding postures are mainly suspensory and seated, short resting postures are suspensory, seated and standing, and long resting postures are almost entirely seated and reclining. Twigs are the most important supports in feeding postures, but branches are much more important in resting postures. The results of this study indicate that the quadrumanous climbing, forelimb-dominated locomotion during feeding that FLEAGLE considers the primary hominoid adaptation is also characteristic of Ateles.