Circumcision may protect against infection with the virus that causes AIDS.

In a study of more than 3,000 young men, those who were circumcised were 65 percent less likely to be infected with HIV compared with those who were not circumcised.

"Circumcision prevented 6 to 7 out of 10 potential HIV infections," says researcher Bertran Auvert, MD, MPH, professor of public health at the University of Versailles-Saint Quentin in France.

Circumcision was so effective at preventing HIV transmission that the trial was stopped early so that all the young men in the study could be offered the procedure, he tells WebMD.

The study included 3,128 uncircumcised young men aged 18 to 24 in a rural area outside of Johannesburg, South Africa. The men were randomly assigned either to undergo the procedure or remain uncircumcised. All the men were heterosexual.

By about 1 1/2 years later, 51 men who had not been circumcised had been infected with HIV, compared with only 18 who had the procedure, the study showed.

The findings were presented at a meeting of the International AIDS Society.

Learn More about HIV Prevention

Get the Facts About HIV and AIDS

Too Soon to Recommend Widespread Circumcision

Doctors have long noticed that circumcised men appeared to be at lower risk of HIV infection. But this is the first time that the observation has been confirmed in a well-designed study in which half the men got the procedure and the other half didn't, according to researchers at the meeting.

"These are very exciting new data on the potential of male circumcision to reduce the risk of HIV transmission," says Helene Gayle, MD, president of the International AIDS Society and director for HIV, TB and Reproductive Health at the Bill and Melinda Gates Foundation.

But until the findings are confirmed in other ongoing studies, "it would be premature to recommend widespread circumcision for HIV prevention," she tells WebMD.

Gayle also cautions that men who are circumcised should not develop a false sense of security and use it as an excuse for unsafe sex or other risky behaviors.

Auvert agrees that questions remain. For example, doctors don't yet know if circumcision can help protect against male-to-male transmission of HIV or whether the findings will hold up over the long term.

But if confirmed, the implications are enormous, he says.

Last year, there were 5 million new HIV infections worldwide -- more than in any other year.

More Than 1 Million Americans Living With HIV

Visit WebMD's HIV/AIDS Health Center

By Charlene Laino, reviewed by Michael W. Smith, MD

SOURCES: 3rd IAS Conference on HIV Pathogenesis and Treatment, Rio de Janeiro, Brazil, July 24-27, 2005. Bertran Auvert, MD, MPH, professor of public health, University of Versailles, France. Helene Gayle, MD, president of the International AIDS Society; director for HIV, TB and Reproductive Health at the Bill and Melinda Gates Foundation.