Clinical staging is a tool useful in medical sciences. It assumes the presence of three key elements. Firstly, pathologic indices are progressing in subsequent stages. Secondly, the patients in the individual stages present similar pathological changes. Thirdly, treatment should be most effective in the earlier stages. Such model is particularly well established in the treatment of malignancies. Staging is useful here to define prognosis, to evaluate the results of treatment, facilitate the exchange and comparison of information among treatment centres. There is much data describing a similar model for mental illnesses including schizophrenia. There are two theories supporting the staging model for schizophrenia: the neurodevelopmental hypothesis and allostatic load concept. Both theories make a theoretical premise for creating the staging model for schizophrenia. We can describe at least three stages in the development of a schizophrenic illness: the prodrome, the first episode and chronic phase. Each stage is reflected by anatomical and functional changes in the brain. Therefore, a clinical staging model can describe a development of schizophrenia over time, to help selecting adequate treatments that are particularly relevant to a given stage and to show the relations between known biological markers and psychosocial risk factors and the stage of the illness.