Parasite prevalence and abundance are important factors affecting species’ conservation. During necropsies on a free-living golden-headed lion tamarin (Leontopithecus chrysomelas) and two Wied’s marmosets (Callithrix kuhlii) in the Atlantic Forest of southern Bahia, Brazil, we collected a large number of adult intestinal parasites that we identified as Prosthenorchis elegans. This parasite is pathogenic for Neotropical primates. Prosthenorchis spp. infestation is influenced by diet with increased risk of exposure from ingesting invertebrate intermediate hosts. The biological similarities and sympatric nature of these two nonhuman primates supports that they may harbor similar infectious and parasitic agents.