The 87-year-old Thatcher went to see her doctor after experiencing some discomfort and subsequently had the growth removed, according to longtime adviser Tim Bell.
The operation was "completely satisfactory," Bell said. He said he couldn't go into detail as to the nature of the growth and declined to name the hospital, saying he did not want it to be inundated with calls.
Thatcher, Britain's first female prime minister, has been in fragile health since she suffered a series of small strokes more than a decade ago. Although she has occasionally appeared at private functions, she has not made public statements for some time.
Thatcher was not well enough to join Britain's queen for a lunch with former and serving prime ministers earlier this year, and two years ago she missed an 85th birthday party thrown for her by Prime Minister David Cameron at his official residence at No. 10 Downing Street. But in October she was well enough to mark her birthday with a lunch out in London with her son Mark and his wife.
Thatcher's declining health was a focus of Oscar-winning biopic "The Iron Lady," which premiered last year.
Thatcher served as prime minister from May 1979 until her resignation in November 1990. She was the first leader to win three consecutive elections, dominating British politics throughout the 1980s.
She was a firm supporter of her American ideological peer, President Ronald Reagan, but is a divisive figure in Britain, where the fruits of her legacy are still debated.