According to the principle of the excluded third (tertium non datur) the gender binary divides our social life into two options only: male or female. Similarly, either/or reactions also seem to be applied by people dealing professionally with issues of transsexualism, transgenderism or related statuses. For instance, the history of transsexualism is characterised by attempts to classify transsexual people hierarchically and descriptively. The primary intention was to discriminate between different types of transsexualism to prescribe hormonal and surgical treatment for 'real' transsexual people and to recommend psychotherapy aiming at relieving gender dysphoria for all the others. In this regard, from the early beginnings sexologists have argued about the origins of transsexualism, because the type of origin -the professionals assumed -legitimises a specific kind of treatment, for example psychotherapy for psychological issues and somatic cross-sex treatment for biological issues. Consequently, psychoanalysts and biologically orientated professionals have debated at great lengths about state-of-the-art treatment for transsexual people. Furthermore, to pass as a 'real' transsexual, most of the people concerned presented themselves in a very schematic way.The main focus of this article is the long-standing history of either/or reactions in health care professionals dealing with issues of transsexualism and related states. In addition, it elaborates on the iatrogenic influence on the behaviour of transsexual people of the biases of health care professionals. Finally, in highlighting perspectives of recent trans theory, conclusions important for the debate of current issues are drawn and ideas for the future of care are developed.