The study aims to compare the legal frameworks of Brazil and Argentina regarding the right to gender identity and the use of a preferred name. The methodology employed consisted of a bibliographic review, consulting books, journals, articles, legal doctrine, and case law to provide the necessary foundation for the development of this study. The conclusion of this comparative analysis on the right to gender identity and the use of a preferred name in Brazil and Argentina highlights significant progress, particularly in Argentine legislation, which has proven to be more progressive and inclusive. Argentina’s Gender Identity Law, enacted in 2012, stands as a milestone in guaranteeing rights for trans individuals, allowing for the change of name and gender on official documents without the need for judicial authorization or medical diagnoses, thus ensuring greater autonomy and dignity for individuals. In Brazil, while the use of a preferred name has advanced, especially with the CNJ Resolution No. 270 and the 2018 Supreme Court decision recognizing the right to amend name and gender without surgery, challenges remain. The lack of comprehensive legislation, like Argentina’s, creates legal uncertainties and inequalities in accessing these rights. Moreover, cultural and social barriers persist, hindering the full acceptance and respect for preferred names and gender identity in everyday life.