The aim of the paper is to analyze the case of a man suffering from paranoid schizophrenia who experiences delusions and hallucinations concerning gender change, and to present ashort overview of the literature. The data presented in the case study were collected during a clinical interview, in the six-month diagnostic process. The interview was partly structured; the battery of tests were also used: MMPI-2, SCID-I, SCID-II, IPP, MoCA, and WAIS-R. A case study of a person whose birth-assigned sex was male but who identifies as female. In the diagnostic process, it turned out that he had delusions and hallucinations, which seem to have a dominant impact on the gender incongruence. The results of the tests seem to confirm the hypothesis that the diagnosis of paranoid schizophrenia was right. Taking into consideration the presented case study, it can be stated that, diagnosing transsexualism, it is vital to distinguish it from psychotic disorders.