The 98-year-old was admitted to the King Edward VII Hospital in London this morning.
Prince Philip has been admitted to hospital as a "precautionary measure", Buckingham Palace has said.
The 98-year-old travelled from the Sandringham estate to the King Edward VII Hospital in London for observation and treatment in relation to a pre-existing condition on Friday morning.
In a statement, the palace said: "The Duke of Edinburgh travelled from Norfolk this morning to the King Edward VII Hospital in London for observation and treatment in relation to a pre-existing condition.
"The admission is a precautionary measure, on the advice of His Royal Highness' Doctor."
Phillip retired from public life in August 2017.
He spent decades supporting the Queen and attending events as a representative of the British Royal household.
