LONDON (Reuters) - Britain's Queen Elizabeth left hospital on Monday a day after being admitted with symptoms of gastroenteritis, looking well and smiling as she walked to a waiting limousine.

The 86-year-old monarch, wearing a red coat and broach, shook hands with medical staff on the steps of the King Edward VII hospital in central London before being driven away.

Palace officials said she had first developed symptoms of the stomach bug on Friday and that the decision to take her to hospital was a precautionary measure.

All the queen's engagements this week, including a trip to Italy scheduled for March 6-7, have been canceled or postponed because of her illness.

It is unusual for the monarch, who is very diligent in carrying out her royal duties, to cancel any engagement.

The head of state, who last year celebrated 60 years on the throne, is known for her robust health. She was last hospitalized in 2003 when she had a knee operation.

(Reporting by Tim Castle; editing by Michael Holden)