AbstractWe investigated demographic changes in three primate species (Alouatta guariba,Sapajus nigritus, andCallithrix flaviceps) at the Reserva Particular do Patrimônio Natural–Feliciano Miguel Abdala, Caratinga, Minas Gerais, Brazil, following a yellow fever outbreak (YFO) by comparing their population sizes before (2015) and after the outbreak (2017–2018), and by monitoring the size, composition, and reproductive status of groups from 2017 to 2021. Comparisons of pre‐ and post‐YFO census data indicate theA. guaribapopulation declined by 86.6%, from an estimated minimum of 522 individuals to 70 individuals. However, by October 2021, the population had grown to at least 86 individuals, with an adult sex ratio (N = 53) that was female‐biased (0.61). Eleven of the 13 groups being monitored systematically were reproductively active with high survivorship to 12 months of age.S. nigritusdeclined by 40%, from 377 to 226 individuals. The sex ratio of 33 adultS. nigritusis also female‐biased (0.71), and at least 8 of 15 groups being monitored are reproductively active.C. flavicepsdeclined by 80%, from 85 individuals to the 15–17 individuals observed from 2017 to 2021. The female‐biased adult sex ratio and presence of infants and juveniles in theA. guaribaandS. nigritusgroups are encouraging signs, but there is still great concern, especially forC. flaviceps.Continued monitoring of the demographics of these primates is needed as their persistence appears to still be at risk.