Euan Blair has been on holiday with his father
The 22-year-old was admitted to the Queen Elizabeth Hospital, on the outskirts of Bridgetown, on Thursday.
Sources at No 10 say Euan did not undergo surgery and his condition was not serious.
Mr Blair has returned to the UK after a three-week holiday in the Caribbean but his wife Cherie stayed with Euan.
Downing Street says the prime minister has stayed closely in touch.
Internship
Mr Blair delayed joining his wife Cherie and four children on holiday to handle negotiations over the Middle East peace crisis.
Euan recently accepted a place on a two-year Masters course in international relations at Ivy League college Yale.
Earlier this year, he finished an internship in Washington with two members of Congress.
Euan hit the headlines as a 16-year-old when he was arrested for being drunk and incapable.
He was found by police officers in Leicester Square, in London's West End, where he had vomited on the pavement.
Euan Blair, the eldest son of British Prime Minister Tony Blair, has been released from hospital this evening. He was admitted yesterday after complaining of stomach pains. 

The twenty-two year-old was being treated in the Queen Elizabeth Hospital, near Bridgetown. It is not thought that Euan's condition was serious and he did not undergo surgery.

Tony Blair and his family had been holidaying on the Caribbean island for the past three weeks. Mr Blair returned home this morning and he was kept up to date with his son's condition.