Adolescent sexual activity is increasing. Premature sexual intercourse results in high figures of adolescent pregnancy and abortion, as well as in increased risk of sexually transmitted diseases (STDs). Lack of information on the prevention of STDs and poor hygiene in both boys and girls are also main reasons for increased morbidity because of STDs during adolescence. Contraceptive behavior during adolescence varies between countries and communities. It seems, however, that the condom and oral contraceptives (OC) are popular contraceptive methods. Ineffective methods such as periodic abstinence, coitus interruptus, and withdrawal before ejaculation are in use. On the other hand, compliance of adolescents on contraception is poor. The above are additional causes for increasing rates of adolescent pregnancies. Countries providing sexual education programs in schools present lower rates of pregnancy and abortion. Adolescent pregnancy is safe if a careful follow up is accepted by the teenager. A significant number of homeless youth are homosexuals or lesbian adolescents. Most of them are at high risk for HIV infection, AIDS, and STDs. It is concluded that sexual education programs are absolutely necessary to offer adolescents the knowledge on the complications of premature sexual activity, as well as prevention of the undesired pregnancy and STDs.