The Transsexual Phenomenon is a medical textbook published by American endocrinologist and sexologist Harry Benjamin in 1966 with The Julian Press.

Benjamin argues that transvestism and transsexuality are a spectrum of conditions, requiring different treatments that ranged from hormone replacement therapy to surgical intervention (such as orchiectomy).

When initially published, the book was met with a mixed reception but would be later known as the "transsexuals' Bible", a standard for trans care in the medical community.

[3] Overall, Benjamin's work was hugely influential in terms of trans visibility in the medical field and set the stage for transgender studies in the modern day.

In contrast, the transsexual experiences intense discomfort around their body and seeks medical interventions in order to live as the opposite sex.

Benjamin emphasizes that sex change operations are essential to transsexual people (Types 5 and 6), but they are widely inaccessible and denied by healthcare providers.

Childhood conditioning, from a Freudian perspective, appeared to be a very possible explanation, but Benjamin argues that there are too many situations in which an absent father does not lead to homosexuality, transvestism, or transsexualism.

Benjamin next depicts methods of surgical intervention for transsexuals: namely, castration, penis amputation, and vaginoplasty, arguing for their use if a doctor deems it is the only way to help a patient to "a happier future".

[14] He notes several different methods of castration, describing that some surgeons prefer to leave the testicles in their undescended state for fear of legal retribution.

Here, he also creates a set of guidelines for which transsexuals would make "convincing" women, and thus, should qualify for surgery, in his eyes, stating that "a heavy masculine build, a height of six feet or more, and a strong, dark beard were causes for worry and doubt.

[17] The results of these findings pushed Benjamin to conclude, after additional consideration of possible sexual handicaps and a review of the "meager" array of medical literature at the time, that no matter how disturbed a transsexual may still be, they "are better off afterward [an operation] than they were before…"[18] Benjamin also considers the legal aspects of transvestism and transsexuality.

"[21] He describes androgen injection as a useful medication to suppress menstrual periods, as well as total hysterectomy, and double mastectomy when desired.

Written by Benjamin's colleague Richard Green, the penultimate appendix considers the history and mythology of transsexualism in Classical and indigenous society.

The Winter 1966-67 issue of Psychoanalytic Review considered it "worthy of respect as a thoughtful digest of much work and a compassionate view of a phenomenon," but disappointing to psychologists and psychoanalysts.

And though Homophile Studies reported frustration with the book for its unclear audience, and apparent promotion of conversion surgery, The American Journal of Psychotherapy described it as a "literary event", writing that "it is satisfying to see that Benjamin's long plea for the right of transsexuals begin to be successful.

[3] The Transsexual Phenomenon was the first medical text to seriously consider that it was possible for trans people to "successfully" live as the sex and gender they identify with.

In the seminal "The Empire Strikes Back: a Posttransexual Manifesto", Sandy Stone documents: When the first clinics were constituted, Benjamin’s book was the standard reference.

It took a surprisingly long time--several years--for the researchers to realize that the reason the candidates’ behavioral profiles matched Benjamin’s so well was that the candidates, too, had read Benjamin’s book, which was passed from hand to hand within the transsexual community, and they were only too happy to provide the behavior that led to acceptance for surgery.

Benjamin has also been heavily criticized for his endorsements of heteronormativity and cisnormativity throughout the text, his reliance on notions of "passing", his construction of gender success, and his criteria for "male transsexuals" who would make "suitable" women.