Objective: Most previous studies of the prevalence of transsexualism have used data from individuals seeking sex reassignment surgery. New Zealand is unique in that transsexual people can apply to have an 'X' for the sex on their passport if they have a name on their birth certificate that is congruent with the sex opposite to their birth assigned sex, and provide a statutory declaration stating they have lived as a member of that sex.
Method: From information provided by the New Zealand Passports Office, it was ascertained that the prevalence of transsexualism among New Zealand passport holders was at least 1:6364.
Results: The prevalence of male-to-female transsexualism was estimated at 1:3639, and the corresponding figure for female-to-male transsexualism was 1:22,714.
Conclusions: These estimates were higher than most previous estimates of transsexualism prevalence. There was also a larger than expected ratio of male-to-female transsexual people to female-to-male transsexual people (6:1), which could in part be due to female-to-male transsexual people being relatively overrepresented among those transsexual people for whom we did not have data on the direction of sex change, or this may be indicative of the demography of transsexualism in Australasia.