Vigilance behaviour was examined in four groups of white-faced capuchins in Santa Rosa National Park, Costa Rica. In each group, males spent more time vigilant than females. Average time spent vigilant within each group was not significantly correlated with group size, but was negatively correlated with the number of male group members. The alpha male tended to be the most vigilant individual in each group. Males in two of the four groups were more vigilant at waterholes than in other areas; males in two of the three groups having overlapping ranges were more vigilant in areas of overlap. There was a positive correlation between absence of neighbours and level of vigilance in both sexes. Male vigilance appeared to be directed primarily towards males in other groups, rather than towards potential predators or other group members.