One of the largest threats facing primate populations is habitat loss, with typically concomitant results of fragmentation, isolation, alteration, and degradation. Many primates exhibit behavioral and dietary flexibility to cope with these changing environments. Titi monkeys (family Pitheciidae, subfamily Callicebinae) are small-bodied, diurnal platyrrhines inhabiting a wide range of altitudinal and habitat types. Researchers have noted considerable variation in their dietary and feeding ecology; however, it is unclear what role dietary flexibility plays in various habitat types. Here, I present the first data on the feeding and foraging ecology of Plecturocebus oenanthe, a Critically Endangered species, inhabiting a secondary forest in Peru. I examined diet composition, food part selection, food species diversity, and seasonal variation in diet composition and feeding behavior, in relation to relative availability of resources. Overall, the titis consumed mostly fruits (54%), followed by insects (22%), nonreproductive plant parts (17%), flowers (4%), and seeds (1.3%). The titis relied on very few plant species per month and overall. They consumed more insects and flowers during the dry season and more fruit during the wet season, corresponding to higher fruit availability. During the dry season, the titis decreased time spent feeding on fruit, but increased or maintained the number of plant species utilized. The titis were also able to subsist on resources common to secondary habitats or altered habitats, including liana species, hemiparasitic mistletoes, cultivated species, and pioneer species. Understanding the potential dietary flexibility for this species will help researchers to predict the most suitable habitats and floristic composition for this species to develop appropriate conservation management strategies.