Report of a case of a 17-year-old male with oligodendrogliomatous involvement of the brain of 10 years duration with postmortem findings. The neoplasm caused signs of increased intracranial pressure by diffusely spreading through and blocking the subarachnoid space. Diagnostic studies and surgery revealed no mass lesion and suggested the syndrome of "serous meningitis" Further studies revealed a defect in cerebrospinal fluid absorption and the patient''s progressively deteriorating course was temporarily helped by repeated, daily lumbar punctures in the face of intracranial hypertension and papilledema. The patient expired after an arachnoid-peritoneal anastomosis. Literature on similar cases is reviewed and clinical and pathophysiological features of the phenomenon discussed.