The article presents a study on delusory changes in perceiving one’s own body in a patient with mental illness. The story of Daniel Paul Schreber is an example of strongly experienced delusions, which, in the described form are contemporarily attributed to schizophrenia. This story, coming from over one hundred years ago, is still vivid, and actualizes the image of mental illness and suffering connected with it in the thoughts of the reader. The author presents these characteristics focusing mainly on the symptoms of dysmorphognosia or dysmorphophobia, which became an important element of delusional constructs. He describes the nature of the experienced symptoms in detail, documenting them with extensive quotations from „Diary of a mental patient” written by such patient. The study of mental illness presented in the paper reveals the meanders of distorted psyche and some changes that are happening in it under the influence of delusions. It is a study undertaking the issue of describing and understanding the symptoms of mental disorders.