Background: Metabolic syndrome (MS) is a very prevalent condition. Studies that show a positive association between mental diseases and diabetes mellitus and the existence of adverse metabolic effects caused by psychotropic drugs allow the presumption that the occurrence of MS is even greater in psychiatric patients. Objective: The objective of this review is to assess the epidemiological studies about the relationship between MS or its components and mental disorders. Methods: Research was carried out at Medline and Lilacs, searching for articles which presented epidemiological data on the prevalence or incidence of MS and its components in psychiatric populations. Results: Schizophrenic patients or with schizoaffective disorder demonstrated an increased prevalence of MS, between 28,4% and 62,5%; one study, with younger schizophrenic patients, showed a prevalence of 19,4%, however 3.7 times higher than the controls. One study with patients with bipolar disorder showed a prevalence of 30%. Increased prevalence of MS was found in women with a history of depression, but not in men. Conclusion: The prevalence of MS is high in patients with schizophrenia and schizoaffective disorder, and in women with a history of depression.