Social non-human primates are potential animal models for studying changes in social dynamics because they build strong emotional bonds inside the group, much as do humans. The common marmoset, a small neotropical primate, is a suitable model because of its low maintenance cost and high reproductive output in captivity associated with the presence of affiliative relationships among the members of the social group and pair bond formation. The paradigm of involuntary separation is frequently used to study the physiological repercussions of social deprivation. In this review we point out the advantages of using social non-human primates as animal models for studying psychological disorders. We focused on New World primates, adding some original findings for common marmosets. Forty-eight adult individuals (24 females) were monitored over 25 days in two situations: baseline phase and separation phase. Variability in basal cortisol levels was recorded for both males and females, and three types of cortisol profile were drawn for the subjects in this population: high, medium and low. Basal cortisol levels were a predictor of hormonal reactivity to social separation. The animals with low and high cortisol levels were hyper- and hyporeactive to separation, respectively. Significant positive correlations between hormonal reactivity and scent-marking behavior were found for low profile males and females. These findings show that common marmosets display behavioral changes during challenging situations and different cortisol profiles within a population. Thus, this species appears to be a suitable animal model for studying mental disorders associated with high and low responsiveness of the hypothalamic-pituitary-adrenal axis.