Childhood gender nonconformity (CGN) is a phenomenon in which prepubescent children do not conform to expected gender-related sociological or psychologicalpatterns, or identify with the opposite sex/gender. Typical behavior among those who exhibit the phenomenon includes but is not limited to a propensity to cross-dress, refusal to take part in activities conventionally thought suitable for the gender and the exclusive choice of play-mates of the opposite sex.

Multiple studies have correlated childhood gender nonconformity with eventual homosexuality ; in these studies, a majority of those who identify as gay or lesbian self-report being gender nonconforming as children. The therapeutic community is currently divided on the proper response to childhood gender nonconformity. One study suggested that childhood gender nonconformity is heritable.