Sexually transmitted diseases (STDs) are very common in the young, athletic population. Many STDs cause no symptoms, but even when symptoms occur it can be difficult to distinguish between two different infections. Sexual history, current complaints, physical examination, and laboratory tests are all important in determining the cause. Pharmacologic treatment differs by disease, whether or not the patient is pregnant, and, in some conditions, on the stage of the disease. Prevention is as important as treatment, and all patients should be educated about prevention and the risks associated with sexual activity, especially HIV infection.