With the publication of Benjamin's The Transsexual Phenomenon (1966) a new era of research into the spectrum of gender identity disturbances began. This was the first major clinical book to go beyond the single case study and present data on a large number of individuals (n = 172) who had requested evaluation for sex reassignment surgery (whom he labeled "transsexuals"). Of this group twenty (12 per cent) were women. While Benjamin focused primarily on the male transsexual, he noted that "sometime in the future she [the female transsexual] may merit a book devoted to her alone."

The focus of Benjamin's research was on gathering macro psychological data on a large group of transsexual patients so that their various cases could be compared and general issues extracted (to facilitate clinical decisions and management regarding the care of the trans sexual patient). An endocrinologist by profession, but primarily a person with compassion for the transsexual's plight, Benjamin is considered the pioneer investigator into the transsexual phenomenon. While his research was, at times, on shaky methodological grounds, Benjamin had a knack for short term counseling and understood the difficulties in recommending the transsexual for psychological treatment.

Benjamm's conclusions were derived from a retrospective study m which he interviewed large groups of male and female transsexuals. He did not employ a standardized interviewing technique and depended entirely on the patient's honesty through self reports and responses to questionnaires. He also rated his patients (and classified them as being transvestite and transsexual) using a modified scaling approach popularized by Kinney et al. (1948).

In his portrayal of the female transsexual, Benjamin's style was that of a physician sociologist, focusing on such broad issues as: the patient's symptomology; sex life; etiology; physical data; social position; surgery; and counseling. He assumed that the prevalence of female transsexualism was greatly underestimated (secondary to the females's reluctance to openly avow her problems). Female transsexuals were noted to have a strong wish for sex change; a conviction that they were males trapped in female bodies; a hatred for .their breasts and genitals; a propensity for falling m love with feminine, heterosexually oriented women; a wish to be a husband and father; a dislike for lesbians and an anti homosexual attitude. Most of the female transsexuals in his study had been married, and several had children. (see THE TRANSSEXUAL PHENOMENON PART II)