An 18-year-old French woman is in remission from HIV - despite not having taken any drugs against the virus for 12 years.
Doctors have presented the details of her case at an International Aids Society (IAS) conference in Vancouver.
It is the world's first report of long-term remission from HIV in a child.
Experts say big studies are needed to determine why some patients can continue to control the virus after stopping treatment.
The woman was born in 1996, and was passed HIV by her mother - either towards the end of the pregnancy or during childbirth.
Aged three months, she was given four anti-retroviral drugs.
But her family decided to stop the treatment when she was almost six years old.
Twelve years later, the virus levels in her bloodstream are too low to be measured - although doctors have cautioned that this could change.
Dr Asier Saez-Cirion, from the Institut Pasteur, in Paris, said: "It's likely that this girl has been in virological remission for so long because she received a combination of anti-retrovirals very soon after infection.
"With this first, highly documented case of this young woman, we provide the proof of concept that long-term remission is possible in children, as in adults.
"However, these cases are still very rare.
"The woman is living normally. Her case is unique but had gone unnoticed, even among clinicians in France."
Two years ago, a young girl in America - who became known as the "Mississippi baby" - appeared to be free of HIV.
But her remission lasted for just over two years after drug treatment was stopped.
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Prof Sharon Lewin, from the University of Melbourne, in Australia, said: "The French teenager case provides strong evidence yet again of the powerful benefits of starting anti-HIV treatment as early as possible.
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Prof Lewin added: "Important though this case is, I strongly believe that to advance our efforts towards finding a cure for HIV, we need large prospective studies that can nail down who might be able to safely stop anti-viral therapy and keep the virus under control.
