Primates are vulnerable to habitat loss, as most species are forest-dependent. The Caatinga's forest remnants, Brazil, are subject to anthropogenic disturbances and are highly fragmented. Callicebus barbarabrownae is a Critically Endangered primate endemic to the Caatinga. Our study is the first to investigate the effects of habitat amount, fragmentation, connectivity, and edge exposure on C. barbarabrownae density, evaluating the scale of effect of these variables. We surveyed C. barbarabrownae group density in 30 fragments. Using a patch-landscape design and a multiscale approach, we assessed the effects of landscape predictors on primate group density. Density ranged from 0.004 to 0.447 groups/ha, higher group densities than previously reported. The optimal scale of effect encompassed landscapes with radius between 1844 and 2711 m. Primate group density is negatively related with clumpiness index. Callicebus barbarabrownae group density is higher in landscapes with disaggregated patches, indicating groups confinement and concentration in disconnected patches in landscapes with low to intermediate habitat availability, resulting in a potential crowding effect. Organisms in densely populated and isolated areas may face increased intraspecific competition, disease spread, stress levels, modified behavior patterns, and reduced genetic diversity. This scenario raises concerns regarding the long-term viability of C. barbarabrownae populations in such landscapes, which may suffer from extinction debts. It is also possible that some forest patches retain a greater capacity to sustain viable populations than currently estimated, highlighting uncertainties that warrant further investigation. Our study provides a foundation for conservation initiatives to preserve the endemic C. barbarabrownae and other organisms facing landscape changes.