Harry Benjamin was born in Berlin (1885-1986)  he was an endocrinologist doctor. He is renowned for his pioneering work with Transsexualism (later known as Harry Benjamin Syndrome 'HBS'). He received his doctorate in medicine in 1912 in Tübingen for a dissertation on tuberculosis.

Sexual medicine interested him, but it was not a part of his medical studies. His special interest was hormonal research, and thus he became a disciple of Eugen Steinach, whom he visited in Vienna every summer throughout the 1920s and early 1930s. On these occasions, he also took frequent side trips to Berlin, where he visited both Magnus Hirschfeld and Albert Moll and participated in their congresses.

Following an ill-fated professional visit to the United States, the liner in which Harry Benjamin was returning to Germany was caught mid-Atlantic both by the outbreak of the First World War in 1914, and the Royal Navy. Given the choice of a British internment camp, as an "enemy alien", or returning to New York, he used his last dollars to travel back to America, where he made his home for the rest of his life, although he maintained and built many international professional connections and visited Europe frequently when wars allowed.

In 1948, in San Francisco, Harry Benjamin was asked by Alfred Kinsey, a fellow sexologist, to see a child who "assured to be a girl", despite being born male. The mother of the child wished for help that would assist rather than thwart the child. Kinsey had seen nothing of the like previously. Neither had Dr. Benjamin.

This child rapidly led Harry Benjamin to understand that this was a different condition than that of transvestism, under which adults who had such needs had been classified to that time (see for a competent history of earlier cases).

Despite psychiatrists whom Harry Benjamin involved in the case failing to agree amongst themselves on a path of treatment, Harry Benjamin eventually decided to treat the child with oestrogen (Premarin, introduced in 1941), which had a "calming effect".

He helped arrange for the mother and child to go to Germany where surgery to assist the child could be performed, but from where they ceased to maintain contact, much to Harry Benjamin’s regret.

However, Harry Benjamin continued to refine his understanding, in 1954 openly introducing the term Transsexualism in the medical community, and going on to treat several hundred patients with similar needs in a similar manner, often without accepting any payment. (The term `transsexualim' was originally coined by Hirschfeld in 1923).

Carefully selected colleagues of various disciplines, such as psychiatrist John Alden and electrologist Martha Foss assisted him in San Francisco, and plastic surgeon Jose Jesus Barbosa performed genital reconstructive surgery in Tijuana, Mexico. His patients regarded him as a man of immense caring, respect, and kindness, and many kept in touch with him until his death.

The legal, social and medical background to this in the United States, as in many other countries, was often a stark contrast, since wearing items of clothing associated with the opposite sex in public was often illegal, castration of a male was often illegal, anything seen as homosexuality was often persecuted, if not illegal, and many doctors considered all such people (including children) best treated by forced treatments such as drugged detention, electroconvulsive therapy or lobotomy.

Although Harry Benjamin’s 1966 book, The Transsexual Phenomenon, was immensely important as the first large work describing and explaining the affirmative treatment path he pioneered, he had already published papers and lectured to professional audiences extensively.

Publicity surrounding his patient Christine Jorgersen brought the issue into the mainstream in 1952, and led to a great many people presenting for assistance, internationally. Similar cases in other countries (such as that of Roberta Cowell, whose surgery by Harold Gillies in England was in 1951 but was not publicised until 1954; Coccinelle who received much publicity in France in 1958, and April Ashley whose exposure in 1961 by the British tabloid press was reported worldwide) fuelled this. But most of Harry Benjamin's patients lived (and many still live) quiet lives.

In his work, Harry Benjamin believed in a physiological cause or explanation for Transsexualism. He was very much biologically oriented as he himself declared jokingly to Freud in a meeting: "that a disharmony of souls might perhaps be explained by a disharmony of endocrine glands".

Charles L Ihlenfeld worked with Harry Benjamin for 6 years. Dr. Benjamin intended him to become his heir apparent. However, he left the practice to undertake a psychiatric residency. Dr Ihlenfeld has written:

"By and large psychiatrists of this time considered gender dysphoria as a manifestation of significant psychopathology, and considered the treatment Benjamin was then prescribing as psychiatrically contraindicated. Rather than discouraging Benjamin, this response simply reinforced his feeling that psychiatry as a discipline lacked common sense".

Harry Benjamin was married to Gretchen, to whom he dedicated The Transsexual Phenomenon, for 60 years.

The Harry Benjamin International Gender Dysphoria Association (HBIGDA) began in 1979 and it used Harry Benjamin’s name with his personal permission. In his long and distinguished career, Harry Benjamin came to know many famous American and European scientists, scholars, and artists.