Measles is a highly-infectious viral illness.
It can be very serious and cause severe, even life-threatening, complications. Around 20 percent of cases experience one or more complication.
How is it caught?
Measles can be caught through direct contact with an infected person, or through the air via droplets from coughs or sneezes.
It can affect people at any age - although having measles once usually means lifelong immunity to catching it again.
Measles does mainly affect young children, and complications are more common among children under five, those with weakened immune systems or a poor diet.
How common is it?
There was a rapid increase in measles cases here during 2009, with outbreaks in Mid and West Wales, and North Wales.
There were only eight confirmed cases in 2010, 19 in 2011, and a rise to 116 confirmed cases in 2012.
The main symptoms of measles are:
A distinctive red-brown rash
There is no specific treatment for measles.
Treatment is based on alleviating symptoms.
Public Health Wales urges people to contact a doctor if measles is suspected, and anyone with measles should be closely monitored.
Measles is what's known as a 'notifiable' disease in the UK - which means any doctor suspecting a patient has measles has to report it, by law.
Public Health Wales says the measles vaccine as part of the measles-mumps-rubella (MMR) immunisation is highly effective and safe.
It is recommended one dose is given to children aged 13 months, and another at between 3 and 5 years old.