Strokes are becoming more common at a younger age, with about one in five victims now below the age of 55, research in the American Academy of Neurology Journal suggests.
The study followed 1.3 million people in a US region and found 19% of those experiencing a stroke in 2005 were in this age group, up from 13% in 1993.
This is despite a trend of overall falling rates of the condition.
The Stroke Association said the findings were alarming.
Report author Dr Brett Kissela said: "The reasons for this trend could be a rise in risk factors such as diabetes, obesity and high cholesterol."
The study looked at all people over the age of 20 in greater Cincinnati and North Kentucky over three periods in 1993, 1999 and 2005.
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