In a 1985 interview he recalled: I do remember going, as a young person, to a lecture by Auguste Forel, whose book The Sexual Question was a sensation at the time and which impressed me greatly.

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.

[11] Sometime before 1948, he also began maintaining an office in San Francisco where he practiced during the summer of every year (at 450 Sutter Street, Suite 2232),[12] with many of his patients coming from the nearby Tenderloin neighborhood[13]).

Prior to arriving in the United States, Benjamin studied at the Institut für Sexualwissenschaft; from about this time onward he began to encounter and treat patients who he would later describe as transsexuals.

[16] This case rapidly caused Benjamin's interest in what he would come to call transsexualism,[17] realizing that there was a different condition to that of transvestism, under which adults who had such needs had been classified to that time.

[18] Benjamin conducted treatment with the assistance of carefully selected colleagues of various disciplines (such as psychiatrists C. L. Ihlenfeld and John Alden, electrologist Martha Foss, and surgeons Jose Jesus Barbosa,[19] Roberto C. Granato, and Georges Burou).

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

"[22] 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[23] 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.

[25] Gretchen revealed to Charles L. Ihlenfeld that "about six months after they were married Harry brought his mother from Germany to live with them" and that "from then on their bedroom door remained open".

The group consists of therapists and psychologists who devised a set of Standards of Care (SOC) for the treatment of gender dysphoria, largely based on Benjamin's cases, and studies.