Populations of the yellow-tailed woolly monkey (Oreonax flavicauda) persist in increasingly isolated, threatened cloud forests in scattered areas of the departments of San Martín and Amazonas, in northern Peru. No long-term research has been conducted on this species in more than 20 years. The range of O. flavicauda continues to suffer rapid and widespread deforestation. From June to August 2004,I was involved in selecting a site for an extended study of its behavior and ecology. Here I document the species' continued existence and status in the Bosque de Protección (Protected Forest) of Alto Mayo. Three sightings of O. flavicauda provided a group size of 17–20 individuals—higher than previous sightings by Mariela Leo Luna in the early 1980s, who observed an average group size of nine. The difficulty we encountered in finding groups in the study area suggests that yellowtailed woolly monkeys have a large home range. This and its large body size, low density, low reproductive rate, its restriction to cloud forest and its limited geographic range, combined with a high rate of deforestation in the region, make the species especially susceptible to extinction. Urgently needed are a range-wide census of remaining habitat and populations, and educational initiatives and sustainable-use projects to ensure that the Alto Mayo Protected Forest is a truly protected area.