Pope Francis has been admitted to Rome's Gemelli hospital this afternoon for "scheduled surgery" on his colon, Vatican spokesman Matteo Bruni said.
Mr Bruni said the pope, 84, was suffering from "symptomatic diverticular stenosis" of the colon.
The condition can cause recurrent abdominal pain, bloating and changes in bowel habits.
It was not clear when the surgery would take place, but Mr Bruni said another statement would be issued afterwards.
It is the first time the pope has been admitted to hospital since his election in 2013.
The pope appeared to be in fine health several hours earlier when he addressed thousands of people in St Peter's Square for his Sunday blessing and message.
Apart from sciatica, which causes pain in his legs when he walks, the pope has been in relatively good health since his election.
He is sometimes short of breath because a part of one of his lungs was removed following an illness when he was a young man in his native Argentina.
It was also announced today that the pope will visit Slovakia in September after a brief stop in Hungary to celebrate a mass in the capital Budapest.
"I'm happy to announce that from 12 to 15 September ... I will go to Slovakia for a pastoral visit," Francis said.
He added that he would celebrate the closing mass of the 52nd International Eucharistic Congress in Budapest on 12 September.
Francis' visit to Slovakia will include the cities of Bratislava, Presov, Kosice and Sastin, the Vatican said in a statement.