Eaton WW, Pedersen MG, Nielsen PR, Mortensen PB. Autoimmune diseases, bipolar disorder, and non‐affective psychosis. Bipolar Disord 2010: 12: 638–646. © 2010 The Authors. Journal compilation © 2010 John Wiley & Sons A/S. Objective:  Clinic‐based studies of immune function, as well as comorbidity of autoimmune diseases, bipolar disorder, and schizophrenia, suggest a possible autoimmune etiology. Studies of non‐affective psychosis and schizophrenia suggest common etiologies. The objective was to determine the degree to which 30 different autoimmune diseases are antecedent risk factors for bipolar disorder, schizophrenia, and non‐affective psychosis. Methods:  A cohort of 3.57 million births in Denmark was linked to the Psychiatric Case Register and the National Hospital Register. There were 20,317 cases of schizophrenia, 39,076 cases of non‐affective psychosis, and 9,920 cases of bipolar disorder. Results:  As in prior studies, there was a range of autoimmune diseases which predicted raised risk of schizophrenia in individuals who had a history of autoimmune diseases, and also raised risk in persons whose first‐degree relatives had an onset of autoimmune disease prior to onset of schizophrenia in the case. These relationships also existed for the broader category of non‐affective psychosis. Only pernicious anemia in the family was associated with raised risk for bipolar disorder (relative risk: 1.7), suggesting a small role for genetic linkage. A history of Guillain‐Barré syndrome, Crohn’s disease, and autoimmune hepatitis in the individual was associated with raised risk of 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 data suggest that autoimmune processes precede onset of schizophrenia, but also non‐affective psychosis and bipolar disorder.