Pope Francis was admitted to Rome's Gemelli hospital for intestinal surgery on Sunday, the first time he has been in the 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 announced a trip to Slovakia and Budapest for September.
The Vatican said the 84-year-old pontiff was due to undergo the surgery later on Sunday for symptomatic diverticular stenosis of the colon, which tends to affect older people and can cause abdominal pain.
Francis suffers from other ailments, including sciatica. Last year, a bad cold kept him from taking part in a week-long retreat with senior aides south of Rome.
And, in 2014, Francis was forced to cancel several engagements because of what was believed to be a stomach ailment.