New insights into the mating systems of common marmosets suggest that they are mainly monogamous, although polygyny and polyandry occasionally occur. Long-term monitoring of wild common marmosets has shown that some reports of polygynous groups (i.e., groups that contain more than one reproducing female) in fact indicate an unbalanced reproductive output associated with extragroup copulation. In this study we describe the behavioral and hormonal profiles of common marmoset (Callithrix jacchus) females living in three wild monogamous groups (Q, PBf, and T), varying from five to 11 individuals, at Nísia Floresta field station, RN, Brazil. The mating system of the groups was previously characterized in terms of affiliative, sexual, and mate-guarding behaviors. Behavioral data were collected once a week, and fecal samples were collected at least twice a week for 10-16 months, depending on the group. A preferential allogrooming relationship was recorded between dominant males and females. Under field conditions the reproductive inhibition of subordinate females appears to be more behavioral than hormonal, since subordinate females of the three groups ovulated and two conceived during the study. In these cases, the subordinate and dominant females reproduced 1 month apart, and infanticide (one case confirmed and one suspected) appeared to be part of the reproductive strategy of dominant females. Following the infanticide, ovarian inhibition (group T) or emigration and return to the natal group (group PBf) were observed. In the third group (Q) the subordinate female showed hormonal profiles compatible with pregnancy, but no infants were seen. These findings reflect the different alternatives that wild subordinate common marmoset females use to reproduce.