In a study, entitled Aids in Africa, compiled over two years, using over 150 experts, the UN predicts that nearly 90 million Africans could be infected in the next 20 years if the epidemic is not combated. Some 25 million Africans have HIV.
They estimate 89 million new cases of the disease in Africa - or up to 10% of the continent's population - could exist by the year 2030.
$200bn (£105bn) needs to be invested in a committed campaign against HIV/Aids to stop its spread.
Taking this action against HIV/Aids could save 16 million people from dying of the disease and a further 43 million people from contracting it, the UN says. This exceptional crisis has the potential to decimate entire societies and economies; millions of new infections can be prevented if Africa and the rest of the world decide to tackle this together.
Insufficient political will to change behaviour at all levels means millions of Africans are still being infected because there is no other option.
BBC's UN correspondent, Susannah Price, says it demonstrates the dramatic impact government policies could have on the spread of HIV and Aids in Africa.
The report offers three different outcomes of how the disease could affect the continent in 20 years, based on how much money and effort is invested in fighting it.
If funding and policies stay as they are now, a fourfold increase in the total number of people dying from Aids is to be expected.
If international aid to Africa is doubled, investment in health systems increased, agriculture, education and treatment is dramatically improved the total number of deaths would still continue to rise.
The UN offers hope that the effective use of resources could eventually end the Aids epidemic in Africa.
But it warns that current levels of action could see the disease bring the entire continent to its knees.
Simon Wright, of ActionAid, says the future looks bleak and an international committment is vital to fight this epidemic before generations of Africans are lost.