People who suffer migraines are at a higher risk of stroke after surgery, researchers said.
This means that a history of migraines, which affect about one in five people, should be taken into account when weighing the pros and cons of undergoing an operation, said a study in The BMJ medical journal.
"Given the high prevalence of migraine in the general population, the... association (with stroke) carries public health importance," the authors wrote.
A research team from the United States, Denmark and Germany analysed the records of nearly 125,000 surgical patients at Massachusetts General Hospital and two satellite campuses between January 2007 and August 2014.
Of the group, 771 (0.6 percent) suffered a stroke within 30 days of surgery.
Just over eight percent (10,179) of the surgery group had a history of migraine, compared to 11.5 percent (89) of the 771 who suffered a stroke.
The team calculated the risk of stroke at 2.4 attacks for every 1,000 surgeries -- a number which rose to 4.3 in 1,000 for migraine patients.
The risk was highest for those whose migraines had an "aura" -- described as flashing lights or other warning signals experienced before an attack.
According to the World Health Organization, about 6.7 million people died of stroke in 2012. Survivors often suffer long-term disability.
Stroke occurs when blood flow to an area of the brain is cut off due to a clot blocking the path or due to a leak in a blood vessel. Brain cells are starved of oxygen, and die.
Migraine, more common in women, is characterised by a severe headache often associated with disturbed vision, sensitivity to sounds, smells and light, and nausea.
Migraine has long been considered to increase the risk for stroke, the study authors said, but is still widely perceived as a benign condition.
This study was the first to assess whether migraines boost stroke risk after surgery.
"Physicians should be aware of this increased... risk," said the team. And further research was needed into preventing post-operative stroke in migraine sufferers.