Queen Elizabeth II's husband, Prince Philip, was taken to a hospital on Wednesday as a precautionary measure, Buckingham Palace said.
Officials did not provide any details about the cause of the 91-year-old's trip to the hospital, which follows two recent health scares.
Philip, also known as the Duke of Edinburgh, was taken from the royal family's Balmoral estate in Scotland to the Aberdeen Royal Infirmary on the advice of his physician.
The palace said he travelled the 40 miles (64 kilometers) to the hospital by road.
Philip has endured several health problems recently. He was hospitalized for five days in June with a bladder infection that may have been aggravated by his prolonged appearance at a flotilla pageant marking the queen's 60-year reign.
He later resumed royal duties, attending the opening ceremony of the Olympics on July 27, watching his granddaughter Zara Phillips take part in Olympic equestrian competition two days later and carrying out engagements on the Isle of Wight on Monday. He has looked well at recent events despite his advancing years.
He was diagnosed with heart disease in December after experiencing chest pains that required him to spend Christmas in a hospital. He underwent a successful coronary stent procedure and seemed to recover well, resuming a full schedule within several weeks.
Philip is a former naval officer who married the queen in 1947. His health remained robust through his 80s, but he has appeared frailer in recent years.
When he turned 90, he said he was "winding down," and he has cut back on official duties. But he still carries out some engagements, both with his wife and on his own.