Toxoplasmosis is one of the most common parasitic infections in humans, but in most cases it does not cause serious illness; this protozoan can nevertheless cause devastating disease in immunocompromised hosts such as HIV-positive individuals. Only rarely is toxoplasmosis documented in hematological patients, and among them, those who undergo a transplant procedure are more frequently affected. In a retrospective multicenter survey, we collected data on six cases of toxoplasmosis in hematological patients. In the majority of cases, patients had undergone transplant procedures (five had undergone autologous or allogeneic transplantation). This complication needed special care in diagnosis, usually based on serology, neuroradiology, and PCR examination. However, in our experience the appropriate therapeutic approach was successful in the majority of cases.