Background: Spontaneous intracranial hypotension (SIH) is recognized with increasing frequency. A throbbing headache occurring or worsening in the upright position and improving after lying down, a so-called 'orthostatic headache', low cerebrospinal fluid (CSF) pressure, and diffuse pachymeningeal enhancement on brain magnetic resonance imaging (MRI) are the major features of the classic syndrome. These patients, who are admitted with fever, headache, and CSF findings revealing lymphocytic pleocytosis, elevated protein concentration, normal glucose levels, and negative culture results, are prone to be misdiagnosed with aseptic meningitis. The aims of this single-centre retrospective study were to determine the epidemiological, clinical, laboratory, and radiological features of patients initially evaluated as having aseptic meningitis but subsequently diagnosed with SIH, and to touch upon the key points of the differential diagnosis in daily infectious diseases practice. Methods: Patients referred to Cerrahpasa Medical School with a presumed diagnosis of aseptic meningitis or viral meningitis between 1 January 2006 and 1 January 2011 were reviewed. Epidemiological, clinical, laboratory, radiological, and follow-up data obtained from the hospital database were processed. Patients confirmed to have SIH syndrome were included for evaluation. Results: Eleven cases of SIH syndrome were diagnosed during the study period (8 male and 3 female, median age 30 y, range 21 - 44 y). All had headache, hearing changes, and nausea. Vomiting (10/11) and posterior neck pain (9/11) were also frequent. Seven had fever and 5 had a stiff neck. Four cases had lymphocytic pleocytosis, 4 cases had elevated CSF protein concentrations (> 1.5 times the upper limit of normal), and 2 cases had slightly lower CSF glucose levels. Polymerase chain reaction (PCR) analyses of the CSF for Mycobacterium tuberculosis complex, herpes simplex viruses 1 and 2, and enteroviruses were negative in all cases. MRI of the 11 cases revealed signs of spontaneous CSF leaks with diffuse pachymeningeal gadolinium enhancement (11/11), sagging of the brain (9/11), enlargement of the pituitary (6/11), engorgement of the venous structures (5/11), and subdural fluid collections (2/11). CSF leaks were demonstrated by intrathecal magnetic resonance or computed tomography myelography at different levels along the thoracic spine (7/11), cervico-thoracic junction (2/11), and thoraco-lumbar junction (2/11). Autologous blood injection into the spinal epidural space ('blood patch') was performed for treatment. Strict bed rest followed, and all patients recovered fully within a week; no recurrence or complication was observed during the follow-up periods, which ranged from 6 months to 5 y. Conclusions: Findings of fever, headache, and meningeal irritation are generally accepted as the clinical features of meningitis. When CSF findings are not characteristically compatible with bacterial meningitis and particularly when the headache is orthostatic in nature, SIH should also be included in the differential diagnosis. MRI findings are characteristic and clearly contribute to the differential diagnosis between viral meningitis and SIH.