BackgroundThe Vieira's titi monkey (Plecturocebus vieirai) was recently described and characterized as endemic to Brazil. According to the IUCN red list, this species is classified as critically endangered (CR). At the date of the publication of this manuscript, there are no published data on the health aspects of this species.MethodsFor this study, the necropsy, and histopathological data of the mortality of P. vieirai at Sorocaba Zoo (São Paulo, Brazil) were collected and analyzed.ResultsCauses of death diagnosed included disorders of the urinary, gastrointestinal, immune, and circulatory systems.ConclusionsThis study provides information regarding the pathological conditions of P. vieirai and points to urinary and gastrointestinal diseases as the main causes of death in this species at Sorocaba Zoo. These results can help veterinarians who have this species under their care diagnose and deal with it more quickly, increasing the probability of survival.