The aim of this paper was to present basic data about gender identity disorders and psychotic transsexual desires. From time to time in scientific literature there are descriptions of a diagnosis of psychotic disorders in persons previously diagnosed and treated as transsexuals, in whom the transsexual thinking disappears after using antipsychotic agents. Coexistence of transsexualism and schizophrenia causes a lot of doubt--it is observed in scientists opinions but also in the diagnostic criteria of DSM-IV and ICD-10. Moreover, delusions of sex change are probably more frequent than it is thought. It causes, that in some cases the differential diagnosis of psychosis and gender identity disorders may be very difficult. Transsexuals treatment is on one hand connected with expected effects but on the other hand with many serious, often irreversible health consequences (e.g. cardiovascular disease, risk of neoplasma development, infertility, consequences of surgical sex reassignment). That is why the differential diagnosis of transsexualism and schizophrenia should be made carefully and thoughtfully.