Smoking more than 20 cigarettes a day almost triples the chances of suffering a potentially fatal brain haemorrhage, research has shown.
Quitting reduces the danger but heavy smokers who give up tobacco are still twice as much at risk as people who have never smoked.
Researchers in Korea investigated 426 cases of subarachnoid haemorrhage (SAH) between 2002 and 2004.
Patients were compared with a group of 426 people matched for age and sex who had not experienced a brain bleed.
An SAH occurs when a bulge in a weakened artery, called an aneurysm, bursts in the brain.
The chances of surviving are about 50 per cent and victims who live often face a lifetime of disability.
Study participants who smoked were more likely to have suffered an SAH than non-smokers, scientists found.
The more people smoked, the more at risk they were. After adjusting for other factors such as salt intake, weight and family history of diabetes, smokers were on average 2.84 times more likely to have a brain haemorrhage than non-smokers.
Giving up tobacco for at least five years dramatically reduced the overall risk to 59 per cent. But people with a history of heavy smoking - defined as smoking 20 or more cigarettes a day - were still 2.3 times more likely to have an SAH than those who had never smoked.
The research team, led by Dr Chi Kyung Kim, from Seoul National University Hospital, wrote in the Journal of Neurology, Neurosurgery and Psychiatry: "We have demonstrated that cigarette smoking increases the risk of SAH, but smoking cessation decreases the risk in a time-dependent manner, although this beneficial effect may be diminished in heavy smokers.
"To forestall tragic SAH events, our results call for more global and vigorous efforts for people to stop smoking."
Previous long-term research has indicated that the risk of an aneurysm in former smokers disappears after 10 to 15 years. However, these studies were considered too limited or small to draw reliable conclusions.
In the short term, smoking thickens the blood and drives up blood pressure, both of which can raise the risk of a brain bleed, said the researchers.
But smoking also led to permanent changes to the structure of artery walls which may be more pronounced in heavy smokers.