At the start of a 10-day conference in New York, UNAids launched a five-year action plan addressing the gender issues which put women at risk.
One of the key issues, it says, is that up to 70% of women worldwide have been forced to have unprotected sex.
UNAids says such violence against women must not be tolerated.
"By robbing them of their dignity, we are losing the opportunity to tap half the potential of mankind to achieve the Millennium Development Goals," said Executive Director Michel Sidibe.
"Women and girls are not victims, they are the driving force that brings about social transformation," he said.
The agency says that experiencing violence hampers women's ability to negotiate safe sex.
It warns that, nearly 30 years from the beginning of the epidemic, HIV services do not respond to the specific needs of women and girls.
Women, it says, continue to be disproportionately affected by HIV/Aids.
In sub-Saharan Africa, 60% of those living with HIV are women and in Southern Africa, for example, young women are about three times as likely to be infected with HIV than young men of the same age.
The programme - which will include improving data collection and analysis of how the epidemic affects women, and ensuring the issue of violence against women is integrated into HIV prevention programmes - will be rolled out in countries including Liberia.
