Background: Transsexualism is a worldwide phenomenon known from historic sources in virtually every culture. The phenomenon has been studied since the middle of the 20th century. Some researchers maintain that transsexualism is a result of underlying psychiatric morbidity. Results: Most studies conclude that transsexualism is an isolated diagnosis. However, most studies do conclude that the majority of transsexuals has a prevalence of axis 1 and axis 2 on SCID. No reliable figures concerning the epidemology are available, but studies suggest a prevalence from 1:50.000 to 100.000. Most GID children (70%) will become homosexuals, but will not develop lasting gender dysphoria. No definite cause of transsexualism has been established, but one study has identified a biological influence from the bimorphological area of the hypotalamus. Other hypotheses include familiar influence and an abnormal exposion of hormones to the fetus. Psychotherapy has been proven ineffective in curing transsexualism, while SRS (sex reassignment surgery) is executed to good effect. After a thorough examination, the treatment of transsexuals is made in three steps: real-life test, whereby the patient must live as the preferred sex for a year; hormonial therapy; and SRS. Conclusion: Research has established that after an adequate treatment, transsexuals will live successful, happy and productive lives.