Overall new cases of HIV have fallen
Gay men are being urged to get HIV tests more regularly and practise safe sex in a bid to halt the high numbers of new cases in the UK.
The Health Protection Agency made the warning after new diagnoses among gay men topped 2,600 for the third year.
But the figures do seem to have begun to plateau after a surge at the turn of the century.
Overall, the number of new cases hit an estimated 6,840 in 2007 - a fall of 1,400 from the previous year.
The HPA said this was mostly due to a decline in cases among those infected heterosexually in Africa.
But experts said the new cases among gay men was still at worrying levels.
There were 2,630 diagnoses - a slight fall on previous years, but much higher than the annual figures in the 1990s which tended to hover around 1,500.
HPA head of HIV surveillance Dr Valerie Delpech said: "Gay men continue to be the group most at risk of acquiring HIV within the UK.
"We need to reinforce the safe sex message for gay men that the best way to protect yourself from contracting HIV is practising safe sex by using a condom with all new and casual partners."
She also urged more regular testing so treatment could be started earlier and to reduce the risk of transmission to partners.
The figures are only provisional as they also take into account the expected delays in diagnosis.
The Department of Health has announced a review of national HIV prevention programmes.
Genevieve Clark, of the Terrence Higgins Trust, said it was "good news" that the figures for gay men seemed to be levelling off.
But she warned the number of cases was still too high and called for easier access to testing as some places had long waits for access to sexual health clinics.
Deborah Jack, of the National AIDS Trust, said: "It is a concern that HIV diagnoses are still increasing among gay men and heterosexuals infected in the UK.
"Alongside improved prevention we urgently need better HIV testing strategies.
"HIV is often not picked up early enough by health professionals and late diagnoses increase the liklihood of HIV being passed on, as well as greatly reducing the health prospects of people living with HIV."
A Department of Health spokesman said money had been invested in recent years to improve waiting times.