The purpose of this research is to study the right of people to non-identification by anatomical sex. Identification of biological sex is an extremely common practice in society. The first legal act, after the birth with life, is the public registry and the birth certificate in which the identification of the biological sex. Gender as a historical and cultural construction should not be understood as determinant and permanent. The visual inspection as soon as a given child is born is not enough to guarantee their gender identity, and the proof of this is the perception of the Supreme Federal Court (STF) by allowing transsexual people to extrajudicially alter the civil registry by modifying the civil and biological sex without the need for surgical intervention. However, such a faculty will have no effect for people of the fluid gender and no gender, the registration model needs to reflect the multiple representations of the sex/gender system beyond a binarism.