A 37-year-old hemophiliac patient with known, asymptomatic human immunodeficiency virus infection and chronic Chagas' disease was admitted to the hospital complaining of fever and headache. A computed tomographic scan revealed multiple ring-enhancing lesions in both cerebral hemispheres. No antibodies to Trypanosoma cruzi were found in the cerebrospinal fluid. Treatment for toxoplasmosis of the central nervous system, which was considered the most likely diagnosis, was instituted, but the patient died after progressive neurologic deterioration. An autopsy revealed severe meningoencephalitis caused by T. cruzi.