The duchess is said to be in good spirits after the accident
Camilla, the Duchess of Cornwall, has broken her left leg while hill-walking in Scotland, Clarence House has said.
The duchess, 62, suffered a twisted fracture of her left fibula when she fell on Wednesday.
Clarence House said although doctors advised her not to put any weight on the leg, she would continue to carry out all her official engagements.
Camilla had been staying at Birkhall, the Prince of Wales' private home on the Queen's Balmoral estate.
The break was confirmed following an x-ray on Thursday.
Prince Charles was at Balmoral on Wednesday but not with her at the time of the fall, which happened during their annual Easter break at the estate.
The Clarence House website says the couple "enjoy fishing and walking in the Scottish countryside and often undertake engagements in the local area".
But it would not disclose the exact location of the accident or the hospital where Camilla was treated.
In a statement, Clarence House said: "Yesterday while hill-walking in slippery conditions in Scotland, the Duchess of Cornwall took a tumble and hurt her leg...
"Consequently her royal highness is wearing a plaster cast and will be for six weeks."
The BBC's royal correspondent, Nicholas Witchell, said Clarence House advised that this was "not a serious injury" although the duchess's leg is fractured.
The duchess needed help getting down the hill after she fell but she did not realise she had fractured her leg.
Our correspondent said she had an x-ray because the duchess's leg was still sore the morning after it happened.
Clarence House reported her to be in "good spirits", he added.
A twisted fracture is a relatively common injury, according to an expert in accident and emergency treatment.
Martin Shalley, a retired A&E consultant at Birmingham's Heartlands Hospital, said it was "a natural extension of a bad sprain".
"Usually, as the ankle twists, you may damage a ligament and then carry on. Sometimes, rather than the ligament being damaged, the bone cracks."
Mr Shalley, who is former president of the College of Emergency Medicine, added: "It's usually not very serious. It's fairly common. We see it quite often."
He said complications were rare, and although the injury could prove quite painful, sometimes people were not aware they had fractured the bone because they did not bother to have it checked.
The duchess had had to cancel a number of engagements during a tour to eastern Europe recently because of the pain caused by a trapped nerve in her back.
In 2008-2009, The Prince of Wales carried out 658 official engagements, while his wife carried out 225.