11 cases of measles have been reported to the HSE during an outbreak of the illness in Dublin.
The number includes five recently reported cases.
Health officials say they are concerned about the risk facing children who attended Temple Street Children's Hospital on a number of dates over the last few weeks.
In a statement, the HSE said: "If you or your child attended Temple St Children’s University Hospital on any these dates and you or your child develop symptoms of measles please stay at home and phone your General Practitioner (GP) for advice.
"The risk of measles is for up to 21 days after contact with a case. Please do not contact the hospital about attendances on the above dates."
Symptoms of the disease include a high fever, runny nose and a red rash that spreads down the body.
Health officials say the best protection is to be fully vaccinated with the two recommended doses of the MMR (Measles, Mumps, and Rubella) vaccine.