Spontaneous intracranial hypotension is considered a rare disorder. We conducted a study on the frequency of spontaneous intracranial hypotension in the emergency department (ED). We identified patients with spontaneous intracranial hypotension evaluated in the ED of a large urban hospital between 1 January 2003 and 31 December 2006. For comparison, we also identified all patients with spontaneous subarachnoid haemorrhage (SAH). Eleven patients with previously undiagnosed spontaneous intracranial hypotension were evaluated in the ED during the four-year time period. All patients presented with positional headaches and the duration of symptoms varied from one day to three months. None of the patients were correctly diagnosed with spontaneous intracranial hypotension in the ED. During the same time period, 23 patients with aneurysmal SAH were evaluated. Spontaneous intracranial hypotension is more common than previously appreciated and the diagnosis in the ED remains problematic.