More than 100,000 people across Wales may not realise that they are at risk of an asthma attack.
The stark warning comes from leading charity Asthma UK Cymru.
Our Correspondent Joanna Simpson has been speaking to one woman from Swansea whose sister died because of the condition.
The charity's research found:
- 48% of people with asthma don't think they are at risk of an asthma attack
- 89% are wrong about that
- 110,000 in Wales are at risk of a potentially fatal attack
The new figures come from 2,498 Welsh responses to a test set up by Asthma UK.
The charity is urging adults with asthma to take the 'Avoid Asthma Attacks' test.
It says that the test only takes 60 seconds, will reveal someone's risk of having an asthma attack, and tell them how they can reduce it.
- 314,000 people in Wales are currently receiving treatment for asthma - 1 in 10 of the population
- There were 62 deaths from asthma in Wales in 2010
Asthma UK Cymru says it needs to change the attitude that many people have of 'it's just asthma.'
It has launched a campaign called 'Stop Asthma Deaths', which aims to cut down on people taking everyday risks.
The most common ones include: not taking your preventer inhaler every day, ignoring worsening symptoms, and not having a personal asthma action plan.