Hundreds of activists, officials and health workers are attending the first European and Central Asian Aids conference in Moscow.
Aids awareness campaigns have been hotly debated
It was called to formulate a response to one of the fastest growing rates of HIV infection in the world.
Across Eastern Europe and Central Asia, the number of people living with HIV had reached an estimated 1.6 million by the end of last year, the UN says.
The figure had increased tenfold in less than a decade.
People under 30 accounted for 75% of those infected. Ukraine and Russia have most of the region's cases - Russia's HIV epidemic is the biggest in Europe.
The United Nations says that the situation in both countries represents major challenges for prevention, treatment and care.
The head of UNAids, Peter Piot, told the BBC that the rapid spread of HIV in those regions was initially caused by injecting drugs.
"Eastern Europe and Central Asia have the fastest growing HIV epidemic in the history of Aids. We always think of Africa, which of course has the heaviest toll in terms of Aids, but it's here in this region, in all the republics - all the former Soviet republics - that we see this.
"It's driven by injecting drug use in the first place but now, increasingly, also transmission through heterosexual transmissions is occurring."
Fear and mistrust
Mr Piot said the conference was "long overdue". But he praised President Vladimir Putin's recent announcement that the government would be increasing Aids-related spending this year to more than $100m (£53m), the Associated Press reported.
In the 1980s, when HIV was first detected in what was then the Soviet Union, officials portrayed it as something which mainly affected foreigners.
The BBC's James Rodgers in Moscow says that fear and mistrust of outside influence has persisted.
He says Russian politicians have condemned some current anti-HIV campaigns carried out by non-government organisations, accusing them of encouraging prostitution and drug use.
Meanwhile, rates of infection continue to rise.