A transsexual is a person who physically transitions from male to female or vice versa. Usually this desire commences in puberty, but can happen at any point in someone's life. Transsexual people may take on the role of the opposite sex, may practise crossdressing, or may seek a physical change through surgery. This physical change is usually in the form of sex reassignment therapies, such as hormone replacement therapy and sex reassignment surgery to help them align their body with their identified sex or gender.
According to the Wikipedia page on Transsexual:
"Estimates of the prevalence of transsexual people are highly dependent on the specific case definitions used in the studies, with prevalence rates varying by orders of magnitude. In the United States, the Diagnostic and Statistical Manual of Mental Disorders (DSM-V 2013) gives the following estimates: "For natal adult males [MTF], prevalence ranges from 0.005% to 0.014%, and for natal females [FTM], from 0.002% to 0.003%." It states, however, that these are likely underestimates since the figures are based on referrals to specialty clinics.
The Amsterdam Gender Dysphoria Clinic over four decades has treated roughly 95% of Dutch transsexual clients, and it suggests (1997) a prevalence of 1:10,000 among assigned males and 1:30,000 among assigned females.
Olyslager and Conway presented a paper at the WPATH 20th International Symposium (2007) arguing that the data from their own and other studies actually imply much higher prevalence, with minimum lower bounds of 1:4,500 male-to-female transsexual people and 1:8,000 female-to-male transsexual people for a number of countries worldwide. They estimate the number of post-op women in the US to be 32,000 and obtain a figure of 1:2500 male-to-female transsexual people. They further compare the annual incidences of sex reassignment surgery (SRS) and male birth in the U.S. to obtain a figure of 1:1000 MTF transsexual people and suggest a prevalence of 1:500 extrapolated from the rising rates of SRS in the US and a "common sense" estimate of the number of undiagnosed transsexual people. Olyslager and Conway also argue that the US population of assigned males having already undergone reassignment surgery by the top three US SRS surgeons alone is enough to account for the entire transsexual population implied by the 1:10,000 prevalence number, yet this excludes all other US SRS surgeons, surgeons in countries such as Thailand, Canada, and others, and the high proportion of transsexual people who have not yet sought treatment, suggesting that a prevalence of 1:10,000 is too low.
A 2008 study of the number of New Zealand passport holders who changed the sex on their passport estimated that 1:3,639 birth-assigned males and 1:22,714 birth-assigned females were transsexual.
A 2008 presentation at the LGBT Health Summit in Bristol, UK, showed that the prevalence of transsexual people in the UK was increasing (14% per year) and that the mean age of transition was rising.
Though no direct studies on the prevalence of gender identity disorder (GID) have been done, a variety of clinical papers published in the past 20 years provide estimates ranging from 1:7,400 to 1:42,000 in assigned males and 1:30,040 to 1:104,000 in assigned females.
In 2015, the National Center for Transgender Equality conducted a National Transgender Discrimination Survey. Of the 27,715 transgender and genderqueer people who took the survey, 35% identified as "non-binary", 33% identified as transgender women, 29% identified as transgender men, and 3% said that "crossdresser" best described their gender identity." (https://en.wikipedia.org/wiki/Transsexual)