Originally Posted by Wikipedia - Condom

Condoms are widely recommended for the prevention of sexually transmitted diseases (STDs). They have been shown to be effective in reducing infection rates in both men and women. While not perfect, the condom is effective at reducing the transmission of HIV, genital herpes, genital warts, syphilis, chlamydia, gonorrhea, and other diseases.[33]

According to a 2000 report by the National Institutes of Health, correct and consistent use of latex condoms reduces the risk of HIV/AIDS transmission by approximately 85% relative to risk when unprotected. The same review also found condom use significantly reduces the risk of gonorrhea for men.[34]

A 2006 study reports that proper condom use decreases the risk of transmission for human papilloma virus by approximately 70%.[35] Another study in the same year found consistent condom use was effective at reducing transmission of herpes simplex virus-2 also known as genital herpes, in both men and women.[36]

Although a condom is effective in limiting exposure, some disease transmission may occur even with a condom. Infectious areas of the genitals, especially when symptoms are present, may not be covered by a condom, and as a result, some diseases can be transmitted by direct contact.[37] The primary effectiveness issue with using condoms to prevent STDs, however, is inconsistent use.[15]