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Background: Toxoplasmosis is one of the most important diseases in humans and animals. Almost one-third of the human population around the world is infected with toxoplasmosis. The agent of this parasitic disease is a protozoan called Toxoplasma gondii (T. gondii) that causes encephalitis in people with suppressed immune systems and abortion, mental retardation and chorioretinitis in the fetus. Alzheimer's disease (AD) is the most important neurodegenerative disease. Objectives: Due to the high prevalence of toxoplasmosis in Iran and evidence on its impact on neurodegenerative diseases, this study was performed to evaluate the T. gondii infection in patients with AD. Patients and Methods: In this case-control study, after selection of alzheimer's patients (APs) referred to Imam Reza psychiatric hospital of Khorramabad, west of Iran, and healthy controls (each group consisted of 87 individuals), using the convenience sampling method and under the supervision of a neurologist, blood samples were taken during July 2014 and January 2015. The collected samples were transferred to the research laboratory of parasitology under cold chain storage and then, the serum samples were separated by centrifugation and were frozen at -20 degrees C until use. The T. gondii IgM and IgG specific antibodies were assessed in serum samples using commercial Enzyme Linked Immunosorbent Assay (ELISA) kits. Results: The overall prevalence of T. gondii infection in patients with AD and the control group, using ELISA assay, was obtained as 66.6% (58/87) and 56.32% (49/87), respectively (P = 0.99). In this study, there was no significant association between T. gondii infection and AD. On the other hand, no statistically significant difference was observed between the two groups in terms of infection with T. gondii (P = 0.99). Conclusions: Higher prevalence of T. gondii in patients with AD compared to controls showed the possible impact of this parasite in AD, which may exacerbate symptoms, and this requires special attention of specialists and patient families.