Dr. Harry Benjamin leant medical legitimacy to transsexualism with the publication of The Transsexual Phenomenon in 1966. Using Benjamin's published works and extensive private correspondence with patients, this thesis examines some aspects of the development of transgender medicine and the relationship between transgendered people and the medical establishment in parts of the twentieth century. It argues that Benjamin's background in European sexology and sex reform, combined with his determination to consider his patients' expressed needs first, put him in the perfect position to develop new treatments for transgendered people. It demonstrates that his patients actively sought medical assistance and concludes that it was ultimately Benjamin's willingness and ability to work outside the bounds of accepted medicine coupled with his patients' drive to live in the gender of their choice that contributed to a significant shift in how the American medical establishment responded to transgendered people in the twentieth century.