Some Caribbean countries, like Haiti, where 5% of adults are infected, have the second highest Aids problem in the world after sub-Saharan Africa.
Latin American and Caribbean countries attending a major Aids conference in Brazil have been warned they face a mushrooming epidemic.
The executive director of the Joint United Nations Programme on HIV-Aids, Peter Piot, said this could only be stopped by concerted action from governments.
He said Latin American countries needed to face up to issues like gay sex and condom distribution if they hoped to stop the epidemic.
The host country, Brazil, is almost the only place where the spread of the virus has been kept under control.
Gay at particular risk
Dr Piot blamed social conditions across the continent for the rapid spread of the virus.
He said that inequality, violence and discrimination were particularly to blame.
Some Caribbean countries, like Haiti, where 5% of adults are infected, have the second highest Aids problem in the world after sub-Saharan Africa.
But Dr Piot warned that other Latin American countries are not far behind.
In total, the region is known to have 1.6m people infected, but the real figure is probably much higher.
The epidemic has particularly hit gay communities, in some of which the risk of dying is over 50%.
That is unacceptable, said Dr Piot.
Before the start of the conference, he told reporters that most countries in the region spend less than $50,000 a year on prevention aimed at gay communities, an amount he called a joke.
Cheap drugs
One of the few exceptions to this picture is Brazil.
Effective government action was taken there at the start of the epidemic in the mid-1980s, when the country had one of the highest incidence in the region.
Aggressive publicity campaigns and free Aids drugs have almost stopped further spread of the disease.
Brazil is now starting to produce Aids drugs at a fraction of the cost of the big multi-nationals.
Experts hope other developing countries may benefit from this.
The conference is being held in Rio de Janeiro and will last for five days.
The organisers hope it will increase political will in the region to confront the epidemic.