In mammals it has been proposed that complex social environments have selected for sophisticated social strategies. Third-party and more specifically third-party rank relationship knowledge is an important requirement for such strategies, especially in species with a strict hierarchy such as primates. Previous research has demonstrated that female vervet monkeys know the entire female hierarchy within their group, suggesting a detailed knowledge of their surrounding social world. What remains unclear, however, is the extent and detail of such social knowledge in other age/sex classes. We used the same experimental design to test whether females and males also keep track of each other's hierarchy and whether juveniles know about the female hierarchy. Our results suggest that females know about the male hierarchy but that males and juveniles seem to lack such knowledge regarding the female hierarchy. This indicates sex and developmental differences in the extent of social knowledge and especially third-party rank relationship knowledge in vervet monkeys. As a consequence, sophisticated social strategies may most likely be found in adult females in this species.