Sexually transmitted diseases are infections spread from one person to another during sexual relations. Chlamydia trachomatis (chlamydia) and Neisseria gonorrhoeae (gonorrhea) are bacteria that commonly cause sexually transmitted disease in the United States. Both infections can cause symptoms, such as discharge from the vagina or penis, pain with urination, or abdominal pain. However, many people with chlamydia or gonorrhea have no symptoms. In women, chlamydia and gonorrhea infection can cause difficulties in becoming pregnant (infertility). Infections in pregnant women can lead to prematurity, low birth weight, and serious infections in newborns. Information about the frequency of these infections is needed to guide efforts to look for and treat these diseases. Treatment with antibiotics is important to get rid of symptoms, avoid spreading the infection to other people, and prevent complications of the infections.