Spontaneous intracranial hypotension is a rare but well known entity first described by the German neurosurgeon Schaltenbrand. We report the clinical and radiological findings of four patients (2 males, 2 females, mean age 55 years) presenting with this clinical entity and peculiar constant MRI findings. Intense postural headache was present in all patients together with a very low CSF pressure at lumbar tap although none of the patients had any history of recent lumbar puncture, spinal or cerebral surgery or cranio-cervical trauma. MRI revealed in all patients an intense meningeal enhancement and thickening which was most prominent on the dural side of the subdural space. The ventricular system was thin, presenting almost like slit ventricules. A downward shift of the cerebellar tonsils and hemorrhagic subdural collections were also observed in two patients. Biopsy of meninges performed in two patients showed fibrosis of the leptomeninges together with signs of old hemorrhage in one case. We postulate that histologic and radiologic changes are due to chronic subdural bleeding in relation with abnormal displacement of the nervous structures due to intracranial hypotension. The underlying cause of spontaneous intracranial hypotension is rarely established and the course of the disease is benign. Some authors have advocated to perform isotopic cysternography in search for a CSF leak, particularly in the spine, that could be surgically corrected. No such investigation has been conducted yet in our patients because the spontaneous evolution has been mostly favorable.