Four patients are described presenting papilloedema, increased pressure and reduced CSF absorption--caused by either spinal tumours, leptomeningeal carcinomatosis or encephalitis. Remarkably they all had a normal CT without signs of hydrocephalus. A 24-hour intracranial pressure monitoring showed a mean pressure of 30-35 mm Hg, recurrent plateau waves and high occurrence of B waves. Conductance to CSF outflow studied by a constant perfusion test was severely reduced 0.010-0.026 ml min-1 mm Hg-1 (normal greater than 0.12 ml mm Hg-1 min-1). Despite these findings no ventricular enlargement was seen on serial CT scans. The reason therefore remains unknown. Disappearance of papilloedema and a variable clinical improvement followed shunt-insertion.