Sexually transmitted diseases (STDs) can increase risk for acquisition and transmission of HIV via a number of mechanisms, including breaching of mechanical barriers to infection, increased inflammation and higher levels of HIV cellular targets, and increased genital tract HIV levels. Studies in Malawi clinic populations indicate that treatment of STDs can reduce genital tract HIV levels. Work in Africa and India has indicated that genital herpes infection is associated with increased risk of acquisition of HIV and that presence of genital ulcer disease is associated with increased risk of transmission of HIV disease. Acute HIV infection has been found to be more frequent in individuals with active STDs, and co-transmission may be a common phenomenon. Acute HIV infection, which is not currently routinely diagnosed, is associated with increased risk of transmission. Greater efforts are needed in identifying acute HIV infection in STD clinics. This article summarizes a presentation by Myron S. Cohen, MD, at the International AIDS Society-USA course in Chicago in May.