This chapter discusses the costs of sexually transmitted diseases (STD) in both financial and human terms. It explains what Acquired immunodeficiency syndrome (AIDS) is, what causes it, how it is transmitted, and why it is a difficult disease to treat. AIDS is immediately recognized as a feared lethal disease. Without treatment, any STD can result in undesired complications, so the importance of treating syphilis, gonorrhea, and chlamydia with antibiotics cannot be overstressed. The chapter also explains the following STDs, their symptoms, mode of transmission, and treatment: gonorrhea, genital herpes, Chlamydia. It shows why AIDS and genital herpes are more difficult to treat than syphilis, gonorrhea, and chlamydia. Gonorrhea affects the mucous membranes, primarily in the genital and urinary tracts. Symptoms may include a discharge from the penis, vagina, or rectum and burning or itching during urination. Genital herpes causes the eruption of small blister-like vesicles on the skin or mucous membranes.