This article argues that Lili Elbe has been misrecognized as transsexual, just as Man into Woman (1933) has been misread as a transsexual autobiography. It proposes instead that we understand those who sought transition during the first decades of the twentieth century according to early endocrinological understandings of ovarian or testicular grafting as a means of rejuvenation, or of intersex conditions as the origins of both homosexuality and gender variance, as belonging to the prehistory of transsexuality. The article understands “prehistory” not as the stable foundation of contemporary transsexuality or transgender identity but as the crystallization, in a different form, of something whose various elements will eventually shift, be rejected, and/or fuse with new particles to compose what we now know as “transgender.” Prehistory is thus genealogical in the Foucauldian sense. Exploring a disturbing genealogy of transgender that is implicated in eugenics, rather than recovering transgender figures in history, broadens understandings of what medical transition meant in the recent past. More importantly, it centers for transgender history the intertwined biopolitical genealogies of transgender and homosexuality alike.