A 10-year-old previously healthy boy had a 2-day history of headache, nausea, meaningless speech, difficulty in walking, and an itchy rash on the lower extremities. He had head trauma 3 months previously. There was no contact with any animal. He was disoriented, agitated, and hallucinating. There was bilateral minimal papilledema. Neurologic examination revealed a stiff neck, Kernig's sign, and normoactive cranial and deep tendon reflexes. Motor and sensory systems were normal. He had hypernatremia (sodium level, 168 mmol/L), azotemia (blood urea nitrogen level, 24.0 mmol/L), and hyperuricemia (960 μmol/L). Aspartate aminotransferase, alanine aminotransferase, and creatine phosphokinase levels were very high (781 U/L, 2178 U/L, and 25 130 U/L, respectively). Results of a toxicologic screening, a Vidal test, a titer to detect the human immunodeficiency virus, and antibody titers to detect adenovirus and herpes, measles, mumps, and Epstein-Barr viruses were normal. Levels of ammonia in blood, antinuclear antibodies, urine porphyrins, and