London (CNN) -- Former British Prime Minister Margaret Thatcher "has undergone surgery to remove a growth in her bladder" and is currently recovering in the hospital, her spokeswoman, Gillian Penrose, said Friday.
Thatcher, 87, is doing "absolutely fine" after the operation, her spokeswoman said. She was admitted to the hospital Thursday and is expected to be kept overnight.
Britain's only female prime minister, Thatcher served from 1979 to 1990 as leader of the Conservative Party. She was called the "Iron Lady" for her personal and political toughness.
She enjoyed a close friendship and working relationship with the late U.S. President Ronald Reagan, with whom she shared similar conservative views.
Thatcher retired from public life after a stroke in 2002 and suffered several strokes after that.
She makes few public appearances. She missed a reception in honor of her 85th birthday hosted by Prime Minister David Cameron in October 2010 and skipped the unveiling of a statue of Reagan in London in July last year.
Per Nyberg reported from London. Melissa Gray reported from Atlanta.