The context of sexual orientation is based on the facts that the individual is attracted by persons of ther other or of the same sex. The gender identity disorder (GD) and subclinical variants occur in 3 to 4 per cent of children. Transsexualism is characterized by the intensive wish to live, look like and behave as a person of the opposite sex. Causes of the disorders remains uncovered, a biological-maturation explanation prevails since the 80ies. The center responsible for fetal dimorphism of the brain is localized in hypothalamus. Sexual differentiation may be caused by the size of BSTc (bed nucleus of stria terminalis). The gender identity is due to interaction between intrauterine evolution of the brain and the level of gonadotropic hormones. A surgical reconstruction of disorder of sexual identity – transsexualism – remains to be the most suitable treatment. A hormonal preparation is indicated before the operation. The surgical change of sex should be realized by a specialized team uder strict diagnostic and indication criteria.

        Key words: gender identity disorder, biological-maturation theory of transsexualism, bed nucleus of stria terminalis (BSTc), hormonal testosterone or estrogen preparation, surgical reconstruction.