We report the case of a 4 year-old boy who died from cerebral toxoplasmosis while in remission from acute lymphoblastic leukemia. The clinical picture was remarkably insidious and non specific: diagnosis is particularly difficult in immunodepressed patients. Diagnosis was made on seroconversion. No autopsy was performed. An association of sulfadiazine-pyrimethamine is often effective, but the prognosis is poor in the absence of a specific and precocious treatment.