Epidemiologic data have suggested that male circumcision is a major protective factor against male heterosexual HIV transmission and may explain the significant geographic differences in the prevalence of HIV observed within sub-Saharan Africa. To assess the evidence of the protective effect of male circumcision, African studies on its association with HIV infection were reviewed. These studies' systematic lack of control of important confounding factors makes the assessment of the association between male circumcision and HIV transmission very difficult and raises doubt about the validity of the current findings. Randomized trials are needed to determine the true strength of the association. Until then, a decision to recommend mass male circumcision to prevent HIV transmission in sub-Saharan Africa is premature and risky.