Anecdotal reports of predation as well as observed predation attempts and rates of animal disappearance provide some of the most relevant data for evaluating the influence that predation risk may have on primate behavioural ecology. Here, we report rates of disappearance from six groups of red titi monkeys (Callicebus discolor) and two groups of equatorial sakis (Pithecia aequatorialis) followed over a period of four and a half years at a lowland site in Amazonian Ecuador. We also describe the first direct observation of a harpy eagle (Harpia harpyja) preying upon a titi monkey, as well as 3 unsuccessful attacks by tayras (Eira barbara) on titi monkeys and 4 unsuccessful attacks by various raptors on sakis. Our data indicate that pitheciid primates may face a wider array of possible predators than previously recognized, and that titi monkeys and sakis are susceptible to different major classes of predators. Our observations also suggest differences in the sex role during predator defence that could be related to the evolution and maintenance of monogamous systems.