To determinate the importance of intracranial hypertension in central nervous system (CNS) acute infections, we studied intracranial pressure (ICP) in 27 patients, age 45 days to 13 years. Fourteen had meningitis and 13 had encephalitis; all were in deep coma with Glasgow Coma Scale 7 or less. Intracranial hypertension defined by a mean ICP above 15 mmHg, was observed in 12 patients with meningitis (86%) and in 9 with encephalitis (69%). Patients with meningitis exhibited a sudden and severe intracranial hypertension. A striking difference was noted between survivors and non survivors who had a very high maximal ICP with a severe reduction of cerebral perfusion pressure (CPP). Intracranial hypertension occurred in all patients with acute primary encephalitis but in only 3/7 patients with post-infectious encephalitis. ICP monitoring seems to be important in the comatose forms of: (1) bacterial meningitis in the early period (2) herpes encephalitis (3) post-infectious encephalitis with severe status epilepticus.