The health and well-being of adolescents is closely intertwined with their physical, psychological and social development, but this is put at risk by sexual and reproductive health hazards which are increasing in much of the world. Changes in population growth and distribution, the rise of telecommunications, the increase in travel and a decline in the family, as well as a generally earlier start of menarche and later age of marriage are contributing to an increase in unprotected sexual relations before marriage. This, combined with risks from early marriage, result in too early or unwanted pregnancy and childbirth, induced abortion in hazardous circumstances and sexually transmitted diseases, including HIV infection leading to AIDS. With more than half the world's population below the age of 25, and 4 out of 5 young people living in developing countries with inadequate access to prevention and care, there is an urgent need for action. Young women are particularly vulnerable. Mortality and morbidity from early pregnancy whether ending in childbirth or abortion, is much higher for the younger adolescent. Young women, especially those who have less formal education, are more vulnerable to pressures for marriage, or sexual relations before marriage, often with older men. Young people generally lack adequate knowledge about their own development and information on how to get help. Those who could help are rarely trained for working with adolescents, and services which are generally designed for adults or children often deter young people from getting help when they most need it. Policy and legislation relating to sexual and reproductive health issues are often contradictory, and unclear or unenforced.(ABSTRACT TRUNCATED AT 250 WORDS)