Boris Johnson had a "minor routine operation related to his sinuses" under general anaesthetic at a London hospital, No 10 has said.
The prime minister had the operation at 06:00 BST on Monday and was back in Downing Street at 10:00.
A Downing Street spokesman said Deputy Prime Minister Dominic Raab would make any urgent decisions in his place.
And he said Mr Johnson was feeling well, and was due to take meetings on Monday afternoon.
It is understood Mr Raab remains on hand to assist with any major decisions, but Mr Johnson is expected to chair a meeting of his senior ministers on Tuesday morning and travel to a gathering of Commonwealth leaders later this week.
When questioned on how long the prime minister had experienced problems with his sinuses, his spokesperson said he wouldn't comment on Mr Johnson's medical history.
Asked if the prime minister had skipped waiting lists to get his operation, the spokesman said he was "not getting into" that.
The operation - which was carried out on the NHS and had been "scheduled for a while" - was a success and not related to his previous bout of coronavirus.
In April 2020, Mr Johnson spent three nights in intensive care receiving treatment for the virus. He later said it "could have gone either way".
During his hospitalisation and subsequent recovery, Mr Raab - the then foreign secretary - was in charge of running the government.