The HSE says the number of measles cases in an outbreak in Dublin has risen to eleven.
It says it's particularly concerned about children who attended Temple Street Children's Hospital in Dublin recently.
It follows the discovery of five more cases of the infectious disease.
Doctors are advising parents to be on the alert for symptoms if their child was in Temple Street on July 25th, 26th or 27th, or on August 6th.
The HSE says measles can be a serious illness and is highly infectious.
It says the risk of getting the disease lasts up to 21 days after contact.
Dr Helena Murray, specialist in Public Health Medicine, said: “Measles can be a serious illness and is highly infectious.
"The best protection is to be fully vaccinated with two doses of MMR (Measles, Mumps, and Rubella) vaccine.”