The HSE said it has been notified of two confirmed cases of measles in north Dublin.
The source of the measles has not yet been identified.
An outbreak control team is investigating the cases.
All people identified as contacts of the two measles cases are being notified and advised of the risks.
The HSE said the best protection against measles is to be fully vaccinated with two doses of the MMR (Measles-Mumps-Rubella) vaccine.
Those most at risk of catching measles are those who are not fully vaccinated with two doses of the MMR vaccine, such as babies younger than 12 months who are too young to be vaccinated, and those with weakened immune systems.
The HSE has advised that if people have symptoms suggestive of measles, they should stay at home, not go to school, or work and phone their GP.
