Three questions about female-female relationships remain largely unexplored in female-philopatric platyrrhines. First, to what extent is female dominance status dependent on coalitional support? Second, how stable are female dominance hierarchies over multiyear periods? Third, what is the role of allogrooming in servicing long-term social relationships? We addressed these questions using data collected on Cebus capucinus at Lomas Barbudal and Santa Rosa, over a six-year period. Most female-female coalitions against females reinforced the existing dominance hierarchy, but such coalitions were 3–7 times more frequent at Lomas Barbudal than at Santa Rosa. The Lomas Barbudal group's female hierarchy was highly stable throughout the six years of observation, whereas all three of the intensively observed Santa Rosa groups experienced frequent dominance reversals accompanied by physical aggression. In the Lomas Barbudal group, grooming tended to be directed up the hierarchy, and more closely-ranked females groomed at higher rates than distantly-ranked females, whereas these patterns were not consistently found at Santa Rosa. At both sites, grooming was evenly balanced within 67% of female-female dyads, and mothers of young infants received more grooming than other females did. Females did not spend more of their time grooming each other in groups containing more females than in groups containing fewer females, but they distributed their grooming less evenly among their female groupmates in the largest observed group of females. Some of the intersite differences may be attributable to differences in the rate of female mortality or transfer or both.