This study describes a case of adoption by a female tufted capuchin (Sapajus spp.) who spontaneously adopted a newborn immediately after he was abandoned, then raised him successfully with her own infant. For 7 weeks, we observed the adoptive mother, the adoptee (3 days old at the time of adoption) and the biological infant (4 days old) in order to compare the behavior of the female towards each infant. We focused our attention on different maternal behavioral patterns: grooming, carrying and cuddling behaviors, and we also considered suckling and independent locomotion by the infants. Our results showed no difference in the active care of the adoptive mother. The only significant distinction found between the two infants concerned suckling durations, which were seen to be longer for the adoptee than for the biological infant. We suggested that this could be linked to the gender of the infants, the male adoptee having greater need for milk than the biological daughter.