Introduction: Toxoplasma gondii is an obligate intracellular protozoan parasite which infects a wide range of warm-blooded animals and humans. Cancer remains a leading cause of death worldwide, responsible for approximately 13% of global deaths. Worldwide, the prevalence of human infection with T. gondii has been increasing. However, little is known about the epidemiology of T. gondii infection in different cancer patient groups in Iraq. Thus, the objective of the present study was to determine the prevalence of anti-T. gondii antibodies in patients with four different types of cancer (breast, rectum, thyroid, and leukemia). Methods: Blood samples were collected from 300 patients with cancer and 150 apparently healthy controls and the sera were tested for the presence of anti-T. gondii antibodies (IgG and IgM) using enzyme linked immunosorbent assay (ELISA). Results:The prevalence of anti-T. gondii IgG in cancer patients (49.0%) was significantly higher (P < 0.001) than that in controls (19.3%). The highest T. gondii IgG positivity rate was detected in breast cancer group (56.6%) followed by rectal cancer group (54.0%), thyroid cancer group (44.6%) and leukemia cancer group (36.0%). It is interesting to note that three male patients were infected with breast cancer and only one (33.3%) was seropositive with IgG. In rectum, thyroid gland, and leukemia cancer groups, the anti-T. gondii IgG seropositivity was higher in males than in female patients but the differences were significant (P < 0.05) only in rectum and leukemia groups. The highest seropositivity rates were detected in breast, rectal and leukemia cancer patients aged 51 to 60 years. Conclusions: In conclusion, Toxoplasmosis is significantly more prevalent in cancer patients than in apparently healthy volunteers and accordingly we recommend routine screening of all cancer infected patients for IgG anti-Toxoplasma gondii antibodies and treat the seropositive ones.