Britain's Prince Philip, the husband of Queen Elizabeth II, was taken to Aberdeen Royal Infirmary in Scotland Wednesday after the recurrence of a bladder infection, CNN reported.
The 91-year-old Duke of Edinburgh first suffered the problem in June.
He has been admitted for "investigation and treatment" and is likely to remain in hospital for the next few days, the palace said.
The Duke of Edinburgh was taken to the hospital as a precautionary measure, the palace said earlier. He was staying at the royal residence in Balmoral, Scotland, where the queen traditionally spends part of the summer, UK media reports said.
Prince Philip has suffered a couple of health scares in the past year.
Prior to the bladder infection, which Prince Philip contracted in early June, during events marking the queen's diamond jubilee, he spent four nights in a hospital over the Christmas holiday last year for treatment of a blocked coronary artery.