The Duchess of Cambridge, holding a bouquet of yellow roses, smiled as she left King Edward VII Hospital with her husband, Prince William. She stepped into a waiting car.
She is said to be headed to Kensington Palace to rest. The Duchess had been in the hospital since Monday. St. James's Palace says she is not yet 12 weeks pregnant with the couple's first child. A due date has not been announced.
The Duchess has hyperemesis gravidarum, a very serious condition that causes severe vomiting and dehydration. It affects about 3 1/2 out of every 1,000 pregnant women. It can be so bad in some cases, that women vomit blood.
Whether boy or girl, the child will be next in line behind Prince William in succession to the throne, Cabinet Office officials have said. A child born to Prince William and the Duchess would be third in line to the throne and a great-grandchild of Queen Elizabeth II. The baby would bump Prince Harry down the line of succession to fourth place.
William visited his wife at the hospital every day, while the world media camped outside to glean any news on the royal pregnancy.
Royal officials were forced to announce the pregnancy on Monday after the Duchess' admission into the hospital.
Wednesday, two Australian radio disc jockeys impersonating Queen Elizabeth II and Prince Charles placed a prank call to the hospital, and persuaded an unwitting nurse to tell them all about the Duchess' condition.
Australian radio personalities Mel Greig and Michael Christian later apologized for the hoax - noting that they were surprised that the call was even put through in the first place.
The royals have been the target of hoax callers before. Canadian disc jockey Pierre Brassard telephoned the Queen in 1995, pretending to be Canadian Prime Minister Jean Chretien.
In a conversation that lasted 15 minutes, Brassard managed to elicit a promise from the monarch that that she would try to influence Quebec's referendum on proposals to break away from Canada.
The Associated Press contributed to this report.