Summary: This article taken a close look at transsexualism, a grave psychiatric pathology that is characterised by a conflictual dissociation between the somatic dimensions of sexuality and the subject's gender identity of which is developed contrary to the subject's physical gender. Having first examined the normal components of physical gender in their mutual intertwining, the author synthesises the principal nosographical, clinical and therapeutic problems of transsexualism. Taken up next for study are the burning ethical and canonical issues linked to this dramatic condition, with particular reference to the discussion concerning the real gender of the person, the surgical correction of the fenotipic sex and the admission of a transsexual to matrimony and to sacred order.