The 91-year-old was taken by ambulance to Aberdeen Royal Infirmary yesterday. He had been staying with the Queen at Balmoral.
It is the third occurence of a bladder infection for Philip this year, the first of which happened just before the Diamond Jubilee concert on the 4th June.
As Admiral and member of the Royal Yacht Squadron, the duke had been taking part in Cowes Week on the Isle of Wight this week, shortly before leaving for Scotland, where it is usual for the royals to spend their summer.
Prince Charles and the Duchess of Cornwall are at their private residence of Birkhall on the Balmoral Estate, while the Earl and Countess of Wessex are at Balmoral with the Queen.