The body is at the forefront of the relationship between space and sexuality, and its materiality is the basis on which social and individual conceptions of sex and gender are constructed. In this paper, we use the notion of body borders to approach the way trans persons experience heteronormativity in their bodies. Defined as those elements placed on body physicality that produce social distinctions and reorganize people's social conditions, body borders are important in the processes of sex differentiation and gender oppression that negatively affect trans persons’ processes of identification/disidentification. Drawing on semi-structured interviews with 10 of 43 trans persons from a wider study, who expressed their gender identities at different levels of intensity, we differentiate between four important body borders: man/woman, puberty, inside/outside and liminal zone. The findings reveal that body borders rely to a great extent on the gaze of others and are problematic for trans persons, especially at the beginning of their transition processes, or when their bodies are perceived as more androgynous. Although the experience of body borders is oppressive and causes conflicts to trans persons, they do not impede them from opening up possibilities for new models of transgender identities which defy non-heteronormative ideals and subvert the current gender regulation, which supports these borders.