Second hand smoke has been linked to disease
Being married to a smoker will significantly raise your risk of stroke, even if you don't smoke yourself, say researchers.
The Harvard University team looked at records of more than 16,000 people.
The American Journal of Preventative Medicine study found the risk rose by up to 72% for some non-smokers.
The stroke dangers to smokers are well known, but there are fewer studies which have explored the risk from passive smoking.
Since the introduction of smoking bans in public places across the UK, the home is now the most likely place for non-smokers to breathe second-hand smoke.
The Harvard study looked at people aged over 50, and their spouses, over a period of, on average, just over nine years.
After the results were adjusted for other factors which could influence stroke risk, non-smokers living in the same house as a smoker were found to be at far greater risk of stroke.
If the person had never-smoked, living with a smoker raised stroke risk by 42%. If he or she had smoked at some point in their lives, but given up, the increase in risk was even higher, at 72%.
Being married to a former smoker did not increase risk, suggesting that this extra risk would fall away if the partner stopped smoking.
Dr Maria Glymour, who carried out the research, said: "These findings indicate that spousal smoking increases stroke risk among non-smokers and former smoker.
"The health benefits of quitting smoking likely extend beyond individual smokers to affect their spouses - potentially multiplying the benefits of quitting smoking."
This advice was echoed by the Stroke Association, which said that passive smokers were nearly twice as likely to have a stroke compared with those not living in a smoky environment.
Joe Korner, from the association, said: "Smoking is a significant risk factor for stroke with a quarter of all strokes being linked to smoking and it can also contribute to high blood pressure which is the single biggest risk factor for stroke.
"We urge people to consider the effects that smoking has on their health and others around them and do all they can to reduce their risk of stroke."