Woolly monkeys have been considered vulnerable to forest fragmentation. However, we found a population of woolly monkeys that has been living in a small forest remnant in Colombian Amazonia, raising questions about which factors determine the persistence or extinction of woolly monkeys in fragmented forests. The main purpose of this investigation was to describe the behavioral ecology of woolly monkeys (Lagothrix lagothricha) in a 136-ha forest fragment in Guaviare, Colombia. We recorded activity patterns, diet, and use of space for three monkey troops by instantaneous sampling on focal animals, and we quantified interindividual distance, between January and December 2008. This group of woolly monkeys spent on average 31.7 % of their time feeding, 32.4 % resting, 34.2 % moving, and 1.8 % in social interactions. Their main feeding items were fruits (57.2 %), followed by leaves (15.5 %), arthropods (15.8 %), seeds (5.2 %), flowers (5.1 %), and others (1.2 %). The three most used plant families for fruit consumption were Moraceae (23.4 %), Fabaceae (16.3 %), and Ulmaceae (8.3 %), and the most important species was Ampelocera edentula (Ulmaceae). We estimated an average daily travel distance of 2,339 m and a home range of 126 ha. We found a negative relationship between the degree of interindividual distance and group size. Most of the studied ecological parameters were within the reported ranges for woolly monkeys in undisturbed habitats. Thus, our evidence indicates that their persistence in fragments does not require drastic behavioral changes. We suggest that fragmentation represents a threat to woolly monkeys when (1) fragments are not productive enough to sustain the population and/or (2) when it leads to a higher hunting pressure on the population.