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Schizophrenia is a very complex psychiatric disorder of unknown etiology, and there is controversy as to whether its name is even appropriate to describe the associated variety of clinical presentations and symptoms. Currently, the diagnosis is essentially based on clinical criteria. These enable a clinical profile to be recognized as encompassing positive symptoms, negative symptoms, disorganization of thinking and behavior, cognitive impairment, mood abnormalities, motor abnormalities, chronic clinical course, and incomplete remissions. The concept has evolved during the past century, and schizophrenia is currently questioned as a single disease entity. Established diagnostic criteria do not mirror the heterogeneity of the disorder. A strategy to deal with clinical heterogeneity in schizophrenia is, perhaps, the adoption of a classification system based on dimensions and stages. An additional strategy to deal with etiological and pathophysiological heterogeneity is to try to identify biomarkers, namely, on the basis of intermediate phenotypes. Despite extensive biological research, the biomarkers for schizophrenia are still lacking.