The 86-year-old monarch had been due to attend a military celebration in the city of Swansea to mark St. David’s Day, the national day of Wales.
“The queen will no longer go to Swansea tomorrow,” a spokesman told AFP on Friday.
“She is experiencing symptoms of gastroenteritis. The queen is currently spending the weekend in Windsor as usual.”
Gastroenteritis is an infection of the stomach and bowel, with common symptoms including vomiting, diarrhoea and dehydration.
The spokesman said that no decision had yet been made on the queen’s trip to Rome scheduled for next Wednesday and Thursday, when she is due to meet Italy’s President Giorgio Napolitano alongside her husband Prince Philip.
“She is currently being assessed and she will be assessed in the coming days,” the spokesman added.
The queen had been due to present St. David’s Day leeks — a national emblem of Wales — to members of 3rd Battalion The Royal Welsh, of which she is colonel-in-chief.
Swansea Council said the ceremony would go ahead as planned with the Lord Lieutenant of West Glamorgan, Byron Lewis in attendance.
The queen had on Thursday presented honours to group of stars from the London 2012 Olympics, including gold-medal winning heptathlete Jessica Ennis, during a ceremony at Buckingham Palace.
The British monarch is known for her robust health and has rarely missed a royal engagement due to ill health in recent years.
She was last forced to pull out of an investiture ceremony — where she presents honours including knighthoods — in October last year due to a bad back.
The monarch also missed a visit to the British Museum in October 2011 after suffering from a cold.
In March 1993, she was forced to cancel several engagements with the flu but in the same month refused to cancel a visit to a handbag factory despite having had three stitches in her left hand after being bitten by one of her corgis.
In 2006 she suffered a strain to her back during her annual summer break at Balmoral which led to her cancelling a tour of Arsenal foootball club’s new stadium.
In recent times there have been more concerns about the health of her husband, the 91-year-old Duke of Edinburgh.
In August last year he spent five nights in Aberdeen Royal Infirmary being treated for a repeat of the bladder infection which had also seen him hospitalised for five nights in June.
He spent four nights at Papworth Hospital in Cambridgeshire, eastern England, in December 2011 following a successful procedure to clear a blocked coronary artery.