Margaret Thatcher, Britain's only woman prime minister, is recovering from an operation to remove a tumour from her bladder, an official said.
“She is going to convalesce privately,” her spokesman was quoted as saying.
Tests will now be carried out to discover whether the tumour was aggressive or superficial.
Her 59-year-old daughter Carol has been visiting Thatcher in the undisclosed London hospital.
Thatcher, dubbed the “Iron Lady”, has only made a handful of public appearances over the past few years. She was too ill to join Queen Elizabeth for a lunch for former prime ministers during the queen's diamond jubilee.