Before condoms can be considered as a prophylaxis for sexually transmitted human immunodeficiency virus (HIV), their efficacy must be considered. This paper reviews evidence on condom effectiveness in reducing the risk of heterosexually transmitted human HIV. A meta-analysis conducted on data from in vivo studies of HIV discordant sexual partners is used to estimate the protective effect of condoms. Although contraceptive research indicates that condoms are 87% effective in preventing pregnancy, results of HIV transmission studies indicate that condoms may reduce risk of HIV infection by approximately 69%. Thus, efficacy may be much lower than commonly assumed, although results should be viewed tentatively due to design limitations in the original studies.