<p>Urban expansion is a global driver of wildlife decline, with cities encroaching into forested areas, leading among other things to habitat loss and fragmentation. This can result in remnant forest patches becoming isolated within anthropogenic mosaics, trapping wildlife unable to move beyond the urban areas. The city of Moyobamba, capital of Peru’s San Martin region, population has increased rapidly since 1970 and is currently estimated at ~ 90,000 people. Moyobamba’s urban forest patches are home to the endemic and Critically Endangered San Martin titi monkey (<i>Plecturocebus oenanthe</i>). We conducted an 18-month survey of primates in 23 urban forest patches to determine the presence of <i>P. oenanthe</i>, evaluate the patch-specific variables influencing its presence, and estimate its population size and density in the remaining green areas of Moyobamba city. <i>Plecturocebus oenanthe</i> was present in 17 patches and was never detected outside of patches. Using triangulation we estimate 26 groups of <i>P. oenanthe</i> in Moyobamba, with an average occupied-patch density of 26.9/km². The number of groups per patch was positively correlated with patch area (<i>p</i> = 0.023) and distance between patches (<i>p</i> = 0.0004), whereas presence and density were not correlated with any other landscape metrics, patch size, or habitat structure. Our results demonstrate that urban forests can support important populations of primates, particularly endemic and threatened species. Therefore, remnant forest patches and green corridors should be prioritized in urban planning strategies to ensure long-term wildlife persistence in rapidly developing landscapes.</p>