Health experts have warned that people "aren't taking the right action at the right time" if they see someone with symptoms of a stroke.
The Stroke Association said that acting fast can make a big difference in the outcome for stroke patients.
Research from 2015 shows that almost a quarter of people (24%) mistakenly believe that you have to wait for two stroke symptoms before calling 999.
The comments from the Stroke Association come as Public Health England began its Act FAST campaign.
The campaign urges people to look out for the following signs and call 999 if they spot one:
:: Facial weakness - can the person smile? Has their mouth or eye drooped?
:: Arm weakness - can the person raise both arms and keep them there?
:: Speech problems - can the person speak clearly and understand what you say?
:: Time - to call 999 for an ambulance if any one of these signs occurs.
Juliet Bouverie, chief executive of the Stroke Association, said: "We know people recognise the signs of stroke but they aren't taking the right action at the right time. A stroke is a brain attack and acting fast makes a huge difference.
"You are more likely to survive a stroke and make a better recovery if you call 999 on spotting any one of the symptoms.
"The quicker you act the more of the person you save."
Professor Kevin Fenton, Public Health England's director for health and wellbeing, said: "Stroke is one of the leading causes of death in the country, and the faster someone experiencing a stroke gets emergency treatment, the more chance that person has of surviving and avoiding serious disability.
"It is crucial to Act FAST when you see any single one of the symptoms of stroke, and do not delay making that all-important 999 call."