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Background: A large number of epidemiological evidence in humans and experimental studies in rodents have hypothesized that Toxoplasma gondii is a potentially relevant etiological factor in some mood disorders. Objectives: The aim of this study was to investigate whether latent toxoplasmosis has any role in mood disorders such as schizophrenia and bipolar disease in Western Iran. Patients and Methods: A total of 170 patients including 85 schizophrenia and 85 bipolar patients referred to the only psychiatric hospital in Lorestan province in Khorramabd city, Western Iran, and 170 healthy volunteers were screened for IgG and IgM anti-T. gondii antibodies by the Enzyme Linked Immunosorbent Assay (ELISA). Structured questionnaires were used to obtain information on risk factors for T. gondii infection. Results: Out of the 170 psychiatric patients, 103 (63.5%) patients were seropositive for IgG antibody and 14 (8.2%) were seropositive for IgM antibody. Of the 85 bipolar patients, 54 (63.5%) and 6 (7%) were found positive for anti-T. gondii IgG and IgM antibodies, respectively; whereas among 85 schizophrenia patients, 49 (57.6%) and 8 (9.4%) samples were found positive for anti-T. gondii IgG and IgM antibodies, respectively. From 170 healthy volunteers, 73 (42.9%) tested seropositive for anti-T. gondii antibodies; 65 (38.2%) tested seropositive for IgG antibody and 8 (4.7%) tested seropositive for IgM antibody. There was a significant difference in T. gondii IgG positivity between the psychiatric patients and control groups (P = 0.009). Several risk factors, which were significantly related to T. gondii seropositivity in psychiatric patients are being in contact with cats (P = 0.004), eating unwashed raw vegetables (P < 0.001), raw-milk/egg consumption (P = 0.001), and drinking clean water (P = 0.035). Conclusions: We concluded that psychiatric patients in general and schizophrenia and bipolar cases in particular had a significantly higher relative frequency of T. gondii infection than healthy individuals of Lorestan Province, Western Iran.