“Cut” or “uncut” is usually a choice for parents of newborns, but circumcision could be a promising HIV-prevention tool. The results of the first large-scale study of heterosexual HIV infection and circumcision confirm long-held speculations that foreskin heightens transmission risk.

The 3,000-man South African trial revealed circumcision to be 65% to 75% effective in preventing woman-to-man HIV transmission—51 of the 69 infected men were uncut. Other studies suggest that the foreskin contains a high density of cells targeted by HIV.

Five-sixths of the world’s men are uncircumcised, so researchers are debating the cut as a public-health measure. “We have so few tools to fight [HIV]— any are welcome,” says Robert C. Bailey, PhD, investigator of an ongoing Kenyan study. “But we should wait for other studies.”

Regardless, cost, access and cultural taboos could hinder a snipping policy. Then there’s the unkindest cut, says George Denniston, MD, of Doctors Opposing Circumcision: “Removing foreskin removes sexual pleasure.” Ouch.