The Queen has been admitted to hospital in London suffering from gastroenteritis, Buckingham Palace said.
The palace said the Queen had been admitted to Edward VII Hospital in London in order to be assessed after experiencing symptoms of gastroenteritis.
She was reportedly in "good spirits", despite being forced to pull out of all engagements for the coming week. This includes a planned trip to Rome.
News of the Queen's illness emerged on Friday evening after she was forced to cancel a trip to Swansea for St David's day.
Gastroenteritis is an infection of the stomach and large intestine, most commonly caused in this country by the norovirus and food poisoning.
A Palace spokesman said: "The Queen is being assessed at the King Edward VII's Hospital, London, after experiencing symptoms of gastroenteritis.
"As a precaution, all official engagements for this week will regrettably be either postponed or cancelled."
It is the first time in ten years that the Queen has been admitted to hospital.