We describe five cases of headache due to spontaneous liquoral hypotension, the syndrome comprising sudden, intense and oppressive orthostatic holocranial headache. The headache improved in the recumbent position and was accompanied by nausea and sometimes vomiting. There was no history of lumbar puncture or previous trauma. CSF tension was low or negative. The CSF showed a raised protein content and increased red and white cell counts. CT scan was normal or showed a slit ventricular system. Improvement was complete three to eight weeks from onset. The treatment consisted of bed rest and oral and parenteral fluid replacement. An isotope cisternography carried out in all patients while the headache was present showed a cisternographic pattern characterized by a combination of premature elimination and failure to detect the isotope at the cerebral convexity. Scan images did not show CSF leakage at any site. This stereotyped reaction pattern suggests that CSF hyperabsorption is the most likely pathophysiological mechanism of this entity.