Subarachnoid hemorrhage (SAH) is bleeding into the subarachnoid space—the area between the arachnoid membrane and the pia mater surrounding the brain. Symptoms may include a severe headache of rapid onset, vomiting, decreased level of consciousness, fever, and sometimes seizures. Neck stiffness or neck pain is also relatively common. In about a quarter of people a small bleed with resolving symptoms occurs within a month of a larger bleed. SAH may occur as a result of a head injury or spontaneously, usually from a ruptured cerebral aneurysm. Risk factors for spontaneous cases included high blood pressure, smoking, family history, alcoholism, and cocaine use. Generally, the diagnosis can be determined by a CT scan of the head if done within six hours of symptom onset. Occasionally a lumbar puncture is also required. After confirmation further tests are usually performed to determine the underlying cause. Treatment is by prompt neurosurgery or radiologically guided interventions. Medications such as labetalol may be required to lower the blood pressure until repair can occur. Efforts to treat fevers are also recommended. Nimodipine, a calcium channel blocker, is frequently used to prevent vasospasm. The routine use of medications to prevent further seizures is of unclear benefit. Nearly half of people with a SAH due to an underlying aneurysm die within 30 days and about a third who survive have ongoing problems. Between ten and fifteen percent die before reaching a hospital.