The number of people living with HIV/Aids in India is around half of previous official estimates, at between 2-3.1 million people, new figures say.
The lower estimate could be attributed to more accurate data
The UN-backed government estimates are sharply lower than earlier figures, the health minister announced on Friday.
Previous estimates from the National Aids Control Organisation (Naco) put the number of HIV cases at 5.2m, while UNAids in 2006 estimated 5.7m cases.
Officials say the lower estimate could be attributed to more accurate data.
"Today we have a far more reliable estimate of the burden of HIV in India," Health Minister Anbumani Ramadoss told a news conference in the Indian capital.
"The results show that there are an estimated two million to 3.1 million people affected with HIV-Aids.
AIDS IN INDIA
India's HIV prevalence rate is now estimated to be 0.36 percent
Around 80,000 HIV-positive people receive free drugs
The government plans 250 Aids treatment centres by 2009
It hopes to carry out HIV tests on 42 million people by 2012
Around 40% of women have not heard of Aids
Figures compiled by UNAids and Reuters
"In terms of human lives affected, the number is still large, in fact very large. This is very worrying for us."
The minister said that India had always been accused of underestimating the number of Aids cases.
"That was a disturbing allegation, and today, we have a far more reliable estimate," he said.
The latest estimates were calculated with the help of international agencies, including the UN and US Agency for International Development.
Correspondents say that India was thought to have the world's biggest HIV-positive caseload, but the new estimate means that South Africa and Nigeria are more severely affected.
India is about to embark on a new and expanded phase of its Aids control programme, with increased funding from the government and from international donors.
Mr Ramadoss said that the prevalence level of the infection was now estimated to be around 0.36 percent of the population of more than a billion people - compared to an earlier estimate of 0.9 percent.
Correspondents say that a reason why the latest Aids estimates are so much lower is because previously the UN reached the 5.7m figure by using hundreds of surveillance centres to test the blood of pregnant women and high-risk groups such as drug users and prostitutes over four months each year.
But more recently a new population-based survey that took the blood samples of 102,000 people among the general public - rather than specific groups - indicated for the first time India's HIV caseload was highly overestimated.
UNAids says such that such surveys are more accurate, as they are "more representative" and generate "more accurate information" for rural areas and the male population.
Campaigners warn there should be no cause for complacency
But voluntary groups running anti-HIV/Aids campaigns say the lower numbers should not allow people to become complacent, as there is still a strong need to curb the spread of the virus in a country with a crumbling government healthcare system.
The head of Naco, Sujatha Rao, said there was no reason to fear that money to fight the Aids virus will be reduced.
She said that huge funding was still needed to test people and prevent HIV infection, in addition to providing treatment for people suffering from the illness.
"There is no question of reducing even a dollar towards the fight against Aids," she said.
Last month, health officials said they were especially alarmed by the growing numbers of pregnant women infected with HIV/Aids in the northern states of Uttar Pradesh (UP) and Bihar.
They are among India's most backward, with huge populations but poor literacy and health services.
Officials say workers who migrate to cities in search of work bring the infection back to the states with them.
They said that unless the state governments got serious about tackling the disease, there could still be an Aids epidemic.