Andrew Stimpson was diagnosed as HIV-positive in August 2002 but tests 14 months later showed the virus had completely disappeared from his body, according to hospital officials.
The 25-year-old, from Largs, on Scotland's west coast, told two British newspapers he felt special and blessed to have been "cured" and pledged to help medics in their fight against the condition, which usually leads to AIDS.
"It's so amazing to think that one day I was staring death in the face and now I am waving it goodbye," Stimpson told the News of the World.
But doctors at the Chelsea and Westminster Hospital in London who carried out the initial tests on Stimpson's blood, were more cautious, stopping short of saying he had been given the all-clear.
"I can confirm that he has a positive and a negative test," said a spokeswoman Sunday. "I can't confirm with you that he's shaken it off, that he's been cured.
"When we became aware of his HIV-negative result, we offered him further tests to help us investigate and find an explanation. So far he has declined to do so."
She added: "We urge him, for the sake of himself and the HIV community, to come in and get tested."
Step towards cure?
On being told the negative results, Stimpson considered suing the hospital for bungling the initial test, it was reported.
But he received a letter from the hospital last month stating there was no case to answer. An investigation had confirmed the blood in all the samples was his and there were no mix-ups.
"Those tests are both accurate, the positive and a negative. They are correct," said the hospital spokeswoman Sunday.
Stimpson said he was suprised at the so-called "spontaneous clearance" - which has been reported anecdotally - because he had given up safe sex with his infected partner, 44-year-old Juan Gomez after the diagnosis.
"I have no idea how I got rid of the virus... But maybe it's all down to some genetics in my immune system - so it's important for me to help with research because it can be a big step forward towards a cure for everyone," he told the News of the World.
Doctor George Kinghorn, an HIV specialist at the Royal Hallamshire Hospital in Sheffield, told the News of the World: "If we can better understand what happened inside Andrew's body, it could prove to be a step towards a breakthrough in beating the HIV virus."
Deborah Jack, chief executive of the National Aids Trust, said: "This appears to be a highly unusual case and without further tests it is impossible to draw any conclusions for people living with HIV.
"The virus is extremely complex and there are many unknowns about how it operates and how people's bodies react to it.
"Therefore, if this case were able to shed further light, it could be extremely valuable for research into treatments or a cure."
Stimpson first went for tests in May 2002 after feeling weak and feverish. They came back negative. However, the virus can take three months to appear in the blood after contraction.
Tests in August that year found an exceptionally low level of
Because he was in the early stages, he did not require medication, but doctors were surprised by his continuing good health.
Repeat tests in October 2003 and ever since have come back negative.