Callitrichids are communal breeders that lack sexual dimorphism, and only a few studies have examined behavioral gender differences among them. The purpose of this study was to investigate gender differences in infant carrying in 16 captive and seven wild common marmoset groups. Our results showed that female-female twin pairs were carried significantly more often by fathers than were male-male and male-female pairs both in the wild and in captivity. We suggest these differences may be related to different reproductive potentials of male and female Callithrix jacchus and possibly to future breeding competition among females.