We report two patients with spontaneous intracranial hypotension. In addition to the cardinal features of a postural headache and a low CSF pressure, the patients also had subdural fluid collections demonstrated by head MRI. In both patients, radionuclide cisternography revealed a CSF leak along the spinal axis and rapid accumulation of radioisotope in the bladder. CSF leakage from spinal meningeal defects may be the most common cause of this syndrome. The headache is a consequence of the low CSF pressure producing displacement of pain-sensitive structures. Associated symptoms, including tinnitus and vertigo, and subdural fluid collections are presumably from hydrostatic changes among intracranial fluid compartments that occur at low CSF pressures. Methods of treatment are identical to those for post-dural puncture headaches. Epidural blood patches and epidural saline infusions have rapidly ameliorated the symptoms of spontaneous intracranial hypotension.