It is well established that predator avoidance is an important selective force shaping animal behavior. Much has been written on predation in diurnal primates, but almost nothing is known about predator-prey interactions in nocturnal primates. Even though there has been evidence to the contrary, it is widely accepted that nocturnal primates, in contrast to diurnal species, are limited to indirect anti-predation strategies. To investigate whether nocturnal primates make risk assessments based on direct predator cues, I conducted field and laboratory experiments with wild brown mouse lemurs (Microcebus rufus) in the rainforest of Ranomafana National Park, Madagascar, over a four year period. Mouse lemurs are subjected to a wide range of predators and suffer very high predation rates. I presented objects, odors, and sounds representing avian, mammalian and snake predators to mouse lemurs that were captured in live traps und released after the experiments. I documented the behavioral responses as a measure of risk perception. Mouse lemurs demonstrated the capability to differentiate between predator and non-predator objects and odors. I found no evidence that mouse lemurs differentiated among predators. It is possible that predation pressure by a wide range of predator types, does not allow for the selection of predator specific recognition or response mechanisms. There were indications that visual information was perceived as a higher indicator of danger than olfactory information. Individual variation in behavioral responses indicated that learning and experience might affect risk perception. Mouse lemurs did not appear to perceive predator calls as indicators of danger, suggesting that there was little selection for acoustic predator recognition. Mouse lemurs are thought to most closely resemble early ancestral primates. A better understanding of their behavior and adaptations will provide more insight into early primate evolution. My findings indicate that the selection for cognitive mechanisms that lower predation risk might have evolved well before the emergence of diurnal primate species. The importance of visual information to mouse lemurs in my experiments suggests that the need to avoid predation might have facilitated the evolution of the high acuity visual system so typical of primates.