Transsexuality is a permanent feeling of uneasiness and non-affiliation to the gender in which a person was born, accompanied with a permanent striving to live and be accepted as a person of the opposite gender. The dysfunction appears in childhood and adult age. There is at least one transsexual male in 30,000 adult men and one transsexual female in 100,000 adult women. The aetiology of the dysfunction is still not elucidated, although there are hints connecting transsexuality with a non-standard hormonal activity in prenatal and short perinatal phase of development, which determines an erroneous sexual organization of the brain. Transsexuals differ with respect to biological gender and gender identity (male-to-female, female-to-male) as well as with respect to sexual orientation (homosexual and non-homosexual). For the majority of operated transsexuals the change of gender is a process which improves the quality of life and psychological health. Offering help to transsexuals is an exceptionally difficult task which demands cooperation of a mental health professional (psychiatrist, psychologist), endocrinologist and a surgeon.