The President Mary McAleese was admitted to hospital last night and is being treated for an infection, Áras an Úachtaráin has confirmed.
A spokeswoman for Mrs McAleese said she had been admitted to the Mater Private hospital in Dublin late last night after she had been feeling "unwell" for a number of days.
"She has an infection for which she is receiving intravenous antibiotics," the spokeswoman said.
It is understood that Mrs McAleese was not taken by ambulance to the hospital as it was not an emergency.
The President's spokeswoman said Mrs McAleese had been visited today by her family.
She said: "She's in good form"
A number of engagements this afternoon were cancelled and Mrs McAleese's schedule for tomorrow has also been cleared.
"We will review it over the coming days," her spokeswoman said.