"I'm fine, I'm fine. I feel fine," Thatcher said as she gingerly made her way through a swarm of cameras.
The former leader was comfortable and feeling rested, said Mark Purcell, a spokesman for London's Chelsea and Westminster Hospital. "The doctors assessed her this morning and say she is OK," he said.
Thatcher, 80, has grown frail in recent years following a series of small strokes, and her public appearances have been rare. She has given up most public speaking on her doctors' advice, but is still greatly admired 15 years after leaving office as the country's first female prime minister.
She was taken to hospital Wednesday afternoon after complaining of feeling faint. She remained overnight as a precaution.
Former Conservative Party leader William Hague said Thursday the party wished her well and said she was a "robust lady."
With her forceful personality, Thatcher dominated British politics as prime minister from 1979-90.
Her free-market philosophy, push to privatize state industries and hard-nosed battles with labor unions redrew Britain's economic landscape. Even Prime Minister Tony Blair, whose Labour Party languished in opposition while Thatcher held office for more than a decade, has adopted many of her free market policies.
Her hard-driving style earned her the "Iron Lady" nickname, a term reinforced to some in 1982 when she led Britain into war against Argentina after it invaded the Falkland Islands.
Thatcher has remained a powerful voice in the party, and the Conservatives have struggled to recover from her resignation in 1990, which was prompted by a revolt among her own ministers.
But there is a sense that her influence is waning. The appointment Tuesday of youthful modernizer