Pope Francis, 84, was recovering in hospital Monday from surgery for an inflamed large colon, a potentially painful condition that could see him bed-bound for several days.
The pontiff was admitted to Rome's Gemelli hospital Sunday for a scheduled operation under general anaesthetic for symptomatic diverticular stenosis of the colon.
Afterwards, Vatican spokesman Matteo Bruni said he had "reacted well to the surgery".
The Vatican press office told AFP on Monday it expected to issue a fresh medical bulletin around midday (1000 GMT).
A week earlier, on the eve of the feast of Saints Peter and Paul, Francis seemed to hint at the upcoming operation, saying: "I ask you to pray for the pope, pray in a special way. The pope needs your prayers".
The Argentine is likely to stay in hospital for at least five days, according to Italian news agency ANSA.
The Vatican said it could not confirm how long the stay would be.
The pontiff has already put his Wednesday general audience on hold for the summer, and has no other official appointments in his calendar until next Sunday, when he is to lead the Angelus prayer.
Italy's Prime Minister Mario Draghi sent Francis "affectionate get well soon wishes" Monday, as did the Grand Imam of Al-Azhar University, Sheikh Ahmed el Tayyeb, who wished him "a speedy recovery".
Francis is in the same suite on the 10th floor of the Gemelli hospital used by Pope John Paul II, according to Catholic website Cruxnow.com.
The late pope underwent surgery there several times, including after an attempt on his life in 1981, and for a tumour in the colon in 1992, it said.
Francis's condition causes potentially painful inflammation of the diverticulum, a pocket that can form on the colon walls and which tend to multiply with age.
"Stenosis" here means an abnormal narrowing of the colon, and patients with diverticulitis may experience lower abdominal pain, fever, or rectal bleeding.
The condition may be caused by high pressure within the colon or a diet low in fibre and high in red meat, according to the American Society of Colon and Rectal Surgeons.
The pontiff had arrived at the clinic in the afternoon accompanied by his driver and one close aide, and Italian media said he was in the operating room a few hours later.
Born on December 17, 1936 in Argentina, Francis lost part of his right lung at the age of 21. He also suffers from a hip problem and sciatica.