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Introduction: Clinical research of immune function, along with the comorbidity of autoimmune diseases, schizophrenia, and bipolar disorder, suggest a likely autoimmune etiology. The aim was to determine the degree to which 30 different autoimmune diseases are antecedent risk factors for bipolar disorder, schizophrenia, and non-affective psychosis. Materials &Methods: From the registry, 2031 cases of schizophrenia, 907 cases of non-affective psychosis, and 992 cases of bipolar disorder were considered. Results: Autoimmune diseases were more associated with schizophrenia. These associations also existed for the broader category of non-affective psychosis. The pernicious anemia in the family was associated with raised risk for bipolar disorder, signifying a small role for genetic linkage. Previous Crohn’s disease, Guillain-Barre' syndrome, and autoimmune hepatitis are associated with bipolar disorder. Conclusions: The familial relationship of schizophrenia to a range of autoimmune diseases extends to non-affective psychosis but not to bipolar disorder. The study observations suggest that autoimmune processes not only precede the onset of schizophrenia, but also non-affective psychosis and bipolar disorder.