From the economist:
...[T]he results of two trials, announced on Wednesday December 13th, conducted in Uganda and Kenya under the auspices of America’s National Institutes of Health (NIH), unequivocally show that circumcision can protect men from infection with HIV, the virus that causes AIDS. The circumcised are half as likely to catch the virus as the uncircumcised. The result is so strong that the NIH has stopped both trials: ethical considerations require that circumcision be offered immediately to the uncircumcised control groups of men in both, should they want it.
Maybe we Jews are onto something.