In the conditions of a very low birthrate present in Central Serbia and Vojvodina, promotion of the reproduction health of the adolescents, the population group whose reproductive behaviour determines the demographic trends in the future, has a great significance. Today, the young most frequently suffer from the diseases caused by their risky behaviour, so it is possible to use prevention to ensure decrease of their spreading. In the field of sexuality, risky behaviour and insufficiently responsible attitude to health often lead to unplanned pregnancies and abortions, as well as to contracting sexually transmitted infections. The paper presents the results of an in-depth research carried out in 2002 in Belgrade, dedicated to the sexual behaviour of the young and related to the knowledge, opinions and behaviour of the young relevant for family planning. The sample included 111 female adolescents 14 to 20 years of age, from Belgrade, who started their sexual activity at the age of 16 or earlier, and who came to The Counseling Centre for the Young of The Republic Centre for Family Planning of The Institute for Health Protection of Mother and Child of Serbia. The research showed that the girls respondents do not have enough knowledge in the field of sexuality, about contraception and sexually-transmitted infections, as well as that their behaviour in that sphere was not responsible enough. Moreover it also showed that there is a possibility to improve that knowledge, develop social skills and responsibility in behaviour. An important conclusion of the research is also the fact that love, family and children occupy a very high position in the value system of the respondents.