Sexually transmitted diseases (STDs) are among the top 10 reportable diseases in the United States. Of the more than 12 million cases annually, approximately 3 million occur in adolescents. An estimated two thirds of cases occur in individuals younger than age 25. Almost half of adolescents report ever being sexually active, and approximately one third are currently sexually active. For a number of biologic and psychosocial reasons, sexually active adolescents have the highest rate of STDs of any sexually active age group. They suffer from the acute manifestations of these diseases as well as complications that place them at risk for some significant long-term negative sequelae, such as infertility, chronic pelvic pain, and cancer. This article reviews the reasons for this increased risk and provides updates on the common STDs that affect adolescents.