High adolescent fecundity principally affects developing countries. In spite of a decrease in the incidence of pregnancies in the developing countries over the past 13 years, the differences that exist with respect to developed countries turn adolescent fecundity into an indicator of the level of development of countries. The impact of adolescent pregnancy is evident in maternal and perinatal morbidity and mortality. Nonetheless, in addition to the age involved in precocious pregnancy, it also reflects previous conditions such as malnutrition, infectious diseases and deficiencies in the health care given to pregnant adolescents. The most important impact lies in the psychosocial area: it contributes to a loss of self-esteem, a destruction of life projects and the maintenance of the circle of poverty. This affects both adolescent mothers and fathers; the latter have been studied very little. Intervention with comprehensive health services and the maintenance of the education of adolescent mothers and fathers prevents repeat pregnancies. Evidence shows success in the prevention of the first pregnancy when the intervention includes comprehensive sexual education, the existence of preferential sexual and reproductive health services for adolescents, the handout of modern contraceptives gauged to the adolescence stage of the subjects and the existence of an information network. There is little research in contraception for adolescents, and for this reason, the indications given are projections of data obtained from adults.