Some recent studies have argued that male genital mutilation is a useful tool in lowering the risk of men getting infected with HIV. But here's a counter-argument:

This paper provides strong evidence that when conducted properly, cross country regression data does not support the theory that male circumcision is the key to slowing the AIDS epidemic. Rather, it is the number of infected prostitutes in a country that is highly significant and robust in explaining HIV prevalence levels across countries. An explanation is offered for why Africa has been hit the hardest by the AIDS pandemic and why there appears to be very little correlation between HIV/AIDS infection rates and country wealth.

Worth a look. More attempts at an explanation for the high rate of HIV-transmission in Africa here.