Background: Toxoplasma gondii is an opportunistic parasitic protozoon, which is a causative agent of serious complications such as encephalitis in immunodeficiency patients. Considering insufficient data on toxoplasmosis in these patients, the present study was conducted to determine the seroepidemiology of T. gondii among immunodeficiency patients. Materials and Methods: This cross-sectional study was conducted on cancer, ADIS, hemodialysis and renal transplant patients (case group) and healthy persons (control group) in Kashan and Qom cities. Totally, 317 serum samples were collected from the case group and 120 samples from the control group. The ELISA method was used to determine the anti-T. gondii IgG and IgM antibodies. Results: Totally, 60.3 of the samples from the case and 33.3 from the control groups were positive for anti-T. gondii IgG (P<0.001). In the case group, only 2 persons (0.6) were positive for anti-T. gondii IgM. The anti-T. gondii IgG detected in immunodeficiency patients was 55.2 in Kashan and 68 in Qom, which were higher than in the control group (P<0.001, P<0.006, respectively). The highest prevalence of T. gondii were seen in 40-59 years old (49.8) and illiterate (60) patients. There was a meaningful correlation between toxoplasmosis and blurry vision and dermal rash (P=0.001 and P=0.003, respectively). Conclusion: The prevalence of T. gondii was higher in different immunodeficiency patients compared to healthy persons. Screening examinations were recommended for the diagnosis and treatment of patients to prevent serious side-effects and health education
