 Since 1989, numerous epidemiological studies have reported a significant association between lack of male circumcision MC and risk for HIV infection through heterosexual intercourse. These results have led to calls for male circumcision to be considered as an additional HIV prevention strategy. However, there is a consensus among the international health community that a randomized controlled trial of MC is needed to control for possible confounding factors. Additionally, known risks associated with MC need further investigation. This study will assess the effectiveness of male circumcision in reducing HIV incidence and will evaluate complications of the MC procedure, changes in sexual behavior following circumcision, and the biological mechanisms by which the foreskin may increase HIV susceptibility. The study will be conducted in Kisumu, Kenya, where the Luo tribe is the main ethnic group and less than 10 of adult men are circumcised. 