It says both children and adults have been affected
The Health Service Executive (HSE) says it has confirmed 17 cases of measles.
There are 12 confirmed cases in Dublin, with most cases in the north of the city, and a smaller outbreak of measles in Meath with five confirmed cases.
It says both children and adults have been affected.
Dr Deirdre Mulholland is director of public health for HSE East. She says measles can be a serious illness and is highly contagious.
"The best protection is to be fully vaccinated with two doses of MMR vaccine."
The HSE advises that everyone should be aware of the possible risk of spread of measles whenever groups of people gather, and particularly when attending healthcare services like GPs or emergency departments.
A Measles Outbreak Control Team is investigating the cases, the HSE adds.
It has also repeated the following advice on measures to control further spread of the illness:
Those who think they may have measles are advised to stay home, phone your GP and stop visitors coming to visit you to prevent the spread of measles.
Pregnant women who have been exposed to measles should seek medical advice as soon as possible.