From the viewpoint of a larger society, butch sexual identity is most often considered as being an/as an imiation of a man, which is a consequence of society's tendency to reproduce the binary sexual system of a woman-man. In the thesis I will show how butch identity is to some extent really limited and structured with the dominant heteronormative context, but is predominantly about expressing an internal sense of gender and authenticity. In the empirical part, I studied the case study of a person who identifies as a butch, investigating the course of development of her gender identity and how this process is influenced by external social factors, especially the family environment and school. I applied the results to the model of butch gender identity formation, which was designed by authors Hiestand and Levitt (2005). My findings only slightly deviate from the phases in the model, especially in the time dimension.