Transsexualism has attracted a great deal of interest, far beyond any practical clinical need as the number of patients involved is relatively small. Extrapolating from Swedish (35) and British (15) figures, about 222 males and 71 female cases in the whole of Canada would be expected, the prevalence figures being one case per 34,000 population for males, and one per 108,000 for females. The interest in transsexualism derives mainly from the light which the study of these rare cases will throw on the general nature and development of gender identity. Why a boy comes to consider himself a boy, or a girl a girl, is hardly ever questioned until the un common deviant from the norm comes to our attention. A better understanding of gender identity, its roots, the factors in fluencing its permanence and so on, will in turn find a practical clinical application in cases of hermaphroditism where the question of gender reassignment quite often arises. Gender Reassignment Surgery Since Hamburger's (11) case of Chris tine Jorgensen the procedure commonly called 'sex change operation' has come to be ^Professor and Chairman,