About 10% of patients with subarachnoid haemorrhage die before they receive treatment, and the death rate within 30 days is about 25% or higher. The morbidity and mortality rate for rebleeding is approximately 50%, the rebleeding rate within 2 weeks is 20-25% and the annual recurrence rate after 6 months is 2-4%.
The most important factors affecting prognosis are the time interval after onset and the level of consciousness, with death and complications occurring mostly within 2 weeks of illness, and the morbidity and mortality rate at 6 months being 71% in comatose patients and 11% in awake patients. Other factors, such as older patients have a poorer prognosis than younger patients; aneurysmal subarachnoid haemorrhage has a poorer prognosis than non-aneurysmal subarachnoid haemorrhage.