Benjamin scale

Harry Benjamin's Sex Orientation Scale (S.O.S.) was an attempt to classify and understand various forms and subtypes of transvestism and transsexualism in biological males. It was a seven-point scale (with three types of transvestism, three types of transsexualism, and one category for typical males); it was analogous to the Kinsey scale of sexual orientation, which also had seven categories. Much like Kinsey's understanding of sexual orientation, Dr. Benjamin understood the nature of gender identity and gender expression not as a discrete scale, but as a spectrum, a continuum with many variations, much more than those featured in the scale. But the scale he developed seemed to be an easy, rational and clinically useful way to diagnose different forms of transsexualism and to distinguish between those who needed surgical and/or hormonal treatment and those who didn't.

Benjamin noted, "It must be emphasized again that the remaining six types are not and never can be sharply separated." Benjamin added a caveat: "It has been the intention here to point out the possibility of several conceptions and classifications of the transvestitic and the transsexual phenomenon. Future studies and observations may decide which one is likely to come closest to the truth and in this way a possible understanding of the etiology may be gained."

Benjamin's Scale references and uses Dr. Alfred Kinsey's sexual orientation scale to distinguish between "true transsexualism" and "transvestism". But it should be noted that the strict relationship between gender identity (Benjamin's Scale) and sexual orientation (Kinsey's Scale) was just a result of the researcher's biases, not his scientific findings.

Modern views
More modern views on gender identity issues differ from original Harry Benjamin's view not only in that they exclude sexual orientation as a criterion for diagnosing and distinguishing between transsexuality, transvestism and other forms of gender variant behavior or expression. Modern views also exclude fetishistic transvestism from this spectrum, as it is a distinct phenomenon, not related to gender identity but related to sexual arousal and fetishism.