Schizophrenia is a disorder characterized by disturbances in perception, thought, volition, socialization, psychomotor behavior and the sense of self. Although patients suffer from schizophrenia start from a point of relative normalcy or subtle impairment, following formal onset most patients experience, to some degree, clinical deterioration. This deterioration is manifest by the development of and increasing severity and persistence of psychotic and negative symptoms, cognitive impairment, and diminished social and functional capacity. The underlying causes of this clinical deterioration are not known, but is generally attributed to progression of the illness and associated with periods of active positive symptoms. The deterioration occurs primarily in the early stages of the illness and it is generally confined to the first 5 years after onset. It also does not progress in a linear fashion. Rather, after a period, patients stabilize at a level where they have persistent symptoms and are impaired in their social and vocational function. Despite the heterogeneity of symptoms among patients and their variability within patients across episodes, two distinct patterns have been discerned in long-term catamnestic studies of schizophrenia patients. First, negative symptoms tend to be less common and severe in the early stages of the illness and to increase in prevalence and severity in the later stages. In the early stages positive symptoms are more likely to dominate the clinical picture. Second, within the constellation of positive symptoms, formed or systematized delusions and hallucinations are more common in the earlier stages of illness, whereas thought disorganization, inappropriate affect, and motor symptoms are more common in the later stages of illness.