Injection drug use is the major mode of HIV transmission in many countries. Injection drug users (IDUs) transmit HIV not only through shared drug injection equipment but also through heterosexual and homosexual transmission and mother-to-child transmission. Studies have shown that peer education programs can reduce HIV risk behavior in IDUs. However, it is not known if reduced HIV risk behavior leads to fewer HIV infections. The purpose of this study is to find out if a peer education program can reduce the number of new HIV infections by changing the behavior of IDUs and their HIV risk contacts.