This study aimed to determine the prevalence of anti-Toxoplasma gondii antibodies in patients with neoplasia. One hundred and eight patients with neoplasia and 108 healthy controls were studied for the presence of anti-T. gondii antibodies using a micro ELISA and peroxidase-labelled anti-human IgG (rabbit) and IgM (goat). Anti-T. gondii IgG antibodies were detected in 68 (63.0 %) patients and in 21 (19.4 %) of the controls, which was a statistically significant difference. In addition, anti- T. gondii IgM antibodies were detected in seven (6.5 %) patients and in one (0.9 %) control. A high percentage of positivity for Toxoplasma antibodies in patients with neoplasia was detected. Therefore, parasitological surveys of this patient group should be periodically performed.