A previously-healthy 16-year-old male presented with fever, headache, lethargy and seizures for a day. A hemogram showed mild lymphocytosis. Spinal fluid analysis revealed 75 leukocytes/mm³ (62% neutrophils, 35% lymphocytes, 3% monocytes) and no growth of micro-organisms in culture. Cerebral imaging studies showed an abnormal bilateral symmetrical appearance of the basal ganglia, which, together with positive IgG and IgM serology for the Epstein-Barr virus, suggested acute encephalitis by this agent (Figure). Some of the differential diagnoses were: hypoglycemia, hypoxia, intoxication (methanol, carbon monoxide, cyanide), herpes simplex infection, infantile bilateral striatal necrosis and central extrapontine myelinolysis 1,2,3,4,5 .