The unusual occurrence, protein manifestations, and often devastating consequences of toxoplasmosis in patients with cancer emphasize the need for clinical acumen in the diagnosis and management of this disorder. Toxoplasmosis in patients with cancer has most commonly been described in association with Hodgkin's disease. It has also been reported, usually in the setting of treatment with antineoplastic agents, in patients with other lymphoproliferative disorders, hematologic malignancies, and solid tumors. In this review, among patients for whom the diagnosis was made early enough to begin specific treatment, conditions of 68% improved; this finding was in marked contrast to the severe morbidity and mortality observed for untreated individuals. The high mortality in the untreated group reflects the general debilitation and severe immunocompromise of these patients. Therefore, although toxoplasmosis contributed to a poor prognosis, it was not necessarily always the proximate cause of death.