Some benefits and costs of resident males to females are examined in white-faced capuchins (Cebus capucinus) at Santa Rosa National Park, Costa Rica. A total of 380 hours of focal data were collected on adults in two groups, between January and July 1991. The results of this study suggest that for females, males provide some greater benefits, and impose some higher costs than do other females. Males are more vigilant than females, and are somewhat more successful in detecting predators. To the extent that predator protection is a major benefit of group living, this benefit seems to derive more from males than from females. Increased contest competition is the major cost of group living, and the study suggests that females bear a higher proportion of this cost than males. More foraging related agonism occurs between males and females than between females, more aggression occurs between than within sexes, and female foraging success is negatively associated with agonistic interactions involving males. However, female foraging success is negatively affected by the proximity of other females, and not by the proximity of males. Differences in the distribution of male benefits and costs according to female dominance rank are suggested.