Titi monkeys (Callicebus spp.) are one of two primate genera that live almost exclusively in groups with one adult-size individual of each sex and exhibit extensive biparental care of offspring. We provide a quantitative description of infant care and pairmate behavior in natural groups of Callicebus discolor that contributes to a limited literature on the behavioral ecology of wild titi monkeys. We collected data during a 3-year period from two social groups living in primary tropical rainforest at the Tiputini Biodiversity Station in Amazonian Ecuador before and after the birth of five infants. In order to evaluate the potential social and energetic costs associated with biparental care of offspring, we examined the relationships between infant care, pairmate behavior, and adult activity budgets. We found that males were almost exclusively responsible for transporting, grooming, sharing food, and playing with infants. As predicted, we found that, following the birth of an infant, adults groomed their partners less, spent less time in contact, and that huddling between pairmates decreased. Contrary to our predictions, after the birth of an infant, females did not increase the time spent feeding, and males did not decrease the time spent moving nor increase their resting time. Overall, our data suggest that the pair may experience social costs during times of intense infant care but that any putative energetic costs associated with infant care are not mitigated by adjusting physical activity. Future studies should investigate energy intake and expenditure, and consider how the variation observed in pairmate social relationships may affect reproductive success.