Previous laboratory studies have indicated that adult talapoin monkeys show sex differences in behavior which contrast with those observed in most other species of Cercopithecinae. The present study examines sex differences in a group of seven captive juvenile talapoins. Juvenile males were more active, less affiliative, more assertive, and more playful than females. They initiated and participated in all major types of social play, were avoided, and were alone more often than females. Juvenile females were more evasive, less playful, more affiliative, and showed more pronounced preferences for partners of their own sex than did males. Females avoided more often than males and avoided males more often than females. They groomed, were in proximity, and in contact more often than males, and performed these behaviors more frequently with females than with males. These characteristics have also been demonstrated in other juvenile monkeys. They occur in species with high degrees of adult morphological dimorphism where they are in accord with adult behavioral differences. They are also found in squirrel monkeys with low dimorphism and adult differences similar to those in talapoins, and in human beings. Thus they are not necessarily predictive of adult behavioral sexual dimorphism.