The Taoiseach, Bertie Ahern, is attending a United Nations High Level Meeting on HIV/AIDS in New York.
The delegates include international heads of state, as well as representatives from civil society and from the private sector.
The session convened a day after the publication of a major UN report that showed the incidence of new HIV infections appears to have stabilised for the first time.
But while progress is being made, thanks to a massive increase in spending, better access to drugs and growing awareness, the report warned that huge problems still remain.
The head of the United Nations agency for combating AIDS, Peter Piot, said HIV infection is the biggest epidemic in modern history.
The UN report found that an estimated 38 million people have the virus but more than half of them do not know it.
25 million AIDS deaths since 1981
AIDS has killed more than 25 million people since it was first recognised in 1981, according to UNAIDS, the UN agency co-ordinating the fight against the disease.
The HIV virus, which precedes the disease, infected 65 million people over the same period.
Sub-Saharan Africa remains by far the worst-affected region, being home to two-thirds of all people living with HIV. Two million people died of AIDS in the region last year and there were 2.7 million new infections.
While the epidemic in South Africa, one of the worst in the world, showed no evidence of a decline, other African countries nonetheless made major progress, according to the report.
