In social animals, the period of immaturity is an important life stage that has profound implications on physical, motor and social development. Parental care is a costly evolutionary strategy, and its intensity varies according to ecological, physiological and social factors. The longer the period of immaturity, the grater the parental investment in that offspring. Aloparental care is a form of care where the caregivers are not the genetic parents of those offspring. Two different hypotheses propose to explain the evolution of such care: kin selection and sexual selection. Primates are among the animals that most present forms of aloparental care. Capuchin monkeys are a New World monkey clade with a high encephalization ratio that has many different forms of social organization within its species. The immaturity period of capuchins represents approximately 10% of their lifespan, and infant care is offered mainly by the mother, though allomaternal care has been observed in some species. Blond capuchin monkeys (Sapajus flavius) are an endangered species endemic to northeastern Brazil, inhabiting a few fragments of Atlantic Forest and Caatinga. The immature phase is a period of high mortality risk for species that bare altricial offspring such as these monkeys. Therefore, it is a critical life stage to understand for effective conservation measures to be developed, particularly for species such as this, which inhabit highly fragmented environments. Little is known about the infancy and juvenile period of S. flavius, so the goal of this study is to describe the form immature care takes place in a group inhabiting an Atlantic Forest fragment in northeastern Brazil. Data on free living animals are essential to understand behaviors that affect an organisms’ development in its natural context. Studying this species, particularly in a fragment where male emigration is hampered by its small size, allows us to see what are the behavioral consequences that occur due to this longer stay with their natal group, and how these males adapt to these conditions of “overpopulation” of philopatric individuals.