Given the destruction that humans are bringing to the natural habitat of colobine monkeys, it is important to understand the factors affecting colobine population dynamics so that effective conservation programs can be planned and put into action. Here we consider the effects of food quality and availability, competition, predation, and disease in determining colobus abundance. We find there is little evidence that natural disasters, predation, or disease play a strong role in regulating colobine numbers, but they can cause dramatic declines in populations at specific points in time and space. Given the difficulty of determining niche overlap and competition, no conclusion can be made regarding the role of interspecific competition in limiting colobine abundance. It seems most likely that colobines are limited by the availability of quality food, but the exact nature of that limitation remains unclear.