Former United States President Bill Clinton says India is now the epicentre of the global HIV/Aids epidemic.
Mr Clinton described the challenge to control the spread of HIV in India as a "breathtaking" but said there was still time to limit the impact of the virus.
Mr Clinton, whose foundation is active in fighting HIV, made his comments in a BBC interview to mark World Aids Day.
The UN estimates that India has the highest number of HIV infections of any nation, 5.7 million people,
"When you've got a billion people, and they are as disparate as the Indians are - disparate languages, different living conditions, different income and education levels - the education challenge and the challenge to overcome the stigma of discrimination is breathtaking," Mr Clinton told the BBC's Damian Grammaticas.
But he said that India's successes in other areas augured well for the challenges ahead.
"If [Indians] will just apply the same commitment and ingenuity to dealing with this that they did to developing and information technology economy, then they'll have the same results.
"This is not rocket science. We know what to do," he said.
HIV in India has already spread beyond high risk groups such as prostitutes.
Migrant workers who travel from remote villages looking for work in the cities are spreading the virus to every corner of the country, our correspondent says.
Even a small further increase in infection rate could mean that up to 25 million Indians contract HIV in the coming years.
On Thursday, Mr Clinton gave details of a new initiative in which two Indian companies will supply 19 antiretroviral drugs for HIV-infected children at a greatly reduced price.
More than 40 million people worldwide are infected with HIV/Aids, the UN says.
The cheap drugs, according to the statement, will be available in 62 developing countries in Africa, Asia, Latin American and the Caribbean.
The Clinton Foundation, set up in 2002, aims to provide technical and financial help to poorer countries struggling to stop the spread of HIV/Aids.