Sexually transmitted infections (STIs) remain a public health problem of major significance in most of the world. Adolescents make up about 20% of the world population, of whom 85% live in developing countries. They are at a greater risk of STIs because they frequently have unprotected intercourse, biologically may be more susceptible to infection, often are engaged in multiple monogamous relationships of limited duration, and face multiple obstacles in accessing confidential health care services. Young people who begin to have sexual intercourse in early or middle adolescence are more likely to develop an STI than those who postpone intercourse until later adolescence or adulthood. The most common STIs among adolescents are chlamydia, gonorrhea, human papillomavirus infection, and trichomoniasis. Unfortunately, lately the incidence of HIV/AIDS and syphilis among adolescents is growing. Comprehensive sex education programs in schools can increase STI knowledge and prevent risky sexual behaviors. Health care providers can promote STI prevention methods, including counseling about safe sex.