Adolescent girls and boys use online networking sites differently, and girls have a higher risk of being harmed by non-adaptive use. The aim of the study was to assess the extent to which adolescents portray themselves according to gender stereotypes on their Facebook profiles. Participants were 623 Facebook users of both sexes who responded to the Bem Sex Role Inventory (BSRI) and the Personal Well-being Index (PWI). In the first step, the adolescents responded to the BSRI with respect to how they view a typical adult in terms of gender stereotypes. In the second step, half of them responded to the BSRI with respect to how they view themselves and the other half responded with respect to their self-presentation on Facebook. The results show that adolescents consider themselves to be less sexually differentiated than a typical adult of their own sex, both in their self-perception and their self-portrayal on Facebook. The study confirms that the psychological well-being of girls decreases considerably with age and that it is associated with a greater degree of masculinity. We conclude that adolescents produce accurate self-representations on their Facebook profiles, and both boys and girls tend to offer a less sexually differentiated self-concept and self-portrayal than that of the typical adult, with a slight preference for masculine traits; moreover, masculinity is associated with a greater degree of psychological well-being.