When they tell you that circumcision prevents HIV and STI's, don't believe them. They are lying.
"...After adjustment for demographic and behavioral risk factors lack of circumcision was not found to be a risk factor for HIV (OR = 0.9; 95% CI: 0.51, 1.7) or STI (OR = 1.08; 95% CI 0.52, 2.26). The odds of HIV infection were 2.6 higher for irregular condom users, 5 times as high for those reporting STI, 6.2 times higher for those reporting anal sex, 2.8-3.2 times higher for those with 2-7+ partners, nearly 3 times higher for Blacks, and 3.5 times as high for men who were single or divorced/separated.
Conclusions: Although there may be other medical or cultural reasons for male circumcision, it is not associated with HIV or STI prevention in this U. S. military population..."
U.S. Navy Finds That Circumcision Does Not Prevent HIV or STIs