"Randomized control trials, including in Uganda, Kenya and South Africa, have shown that circumcision can reduce the transmission of HIV in heterosexual men by as much as 65 percent. Introducing it widely in sub-Saharan Africa, particularly in southern Africa where male circumcision rates are low, could prevent an estimated two million infections in the next ten years and save as many as four million lives over the next 20 years."
http://www.sciencedaily.com/releases/2008/08/080804155120.htm
Earlier Male Circumcision May Help to Slow Rates of HIV, HPV Transmission in South Africa
According to Anna R. Giuliano, Ph.D., program leader in cancer epidemiology at Moffitt Cancer Center in Tampa, Fla., and colleagues in the Netherlands, earlier circumcision of males in South Africa may be a positive step in slowing the spread of both HIV and the human papillomavirus (HPV). Their commentary and data were published in a recent issue of the British medical journal The Lancet Infectious Diseases (Vol. 11) 581-582.
"Countries with high incidences of HIV also have high incidences of cancer-related HPV," said Giuliano. "This is especially true in South Africa."
http://www.sciencedaily.com/releases/2011/10/111006133022.htm
Male Circumcision Reduces HIV Risk: No Further Evidence Needed, According To Review
ScienceDaily (Apr. 15, 2009) — Three recent African trials support male circumcision for reducing the risk of contracting HIV in heterosexual men. After including new data from these trials in their review, Cochrane Researchers have changed their previous conclusions that there was insufficient evidence to recommend circumcision as an intervention to prevent HIV infection in heterosexual men.
http://www.sciencedaily.com/releases/2009/04/090415074940.htm
Circumcision ring cuts AIDS risk in Africa
http://www.msnbc.msn.com/id/35407224/ns/health-aids/t/circumcision-ring-cuts-aids-risk-africa/#.T1MmGnlYWSo
Male circumcision for HIV prevention
http://www.who.int/hiv/topics/malecircumcision/en/