About 10% of the human genome has now been mapped and for more than 1000 diseases closely linked DNA polymorphisms or the responsible genes have been identified. These developments have extended the scope of (prenatal) diagnosis and carrier detection which already was possible by biochemical analysis of protein defects in some 400 Mendelian disorders. Together with the study of chromosomal aberrations these activities form the basis for genetic counselling and carrier screening programmes. A brief overview of the activities in clinical genetics will be presented and their importance for the prevention of congenital disorders and for informed decisions of couples at risk will be emphasized. Reproductive decisions are, however very closely related to culture, religion, education and the socioeconomic status of individuals and populations. Up to now genetic services have mainly been developed in wealthy postindustrial countries with a low infant mortality. But even among these countries there are major differences in the implementation of gene technology as will be shown by comparisons of the United States, Europe and Japan. In the developing countries where about 95% of the world's future children will be born there are major hindrances in the development of clinical genetics such as poverty, illiteracy of women, low contraceptive use and a high infant mortality. There are, however, examples of developing countries that give high priority to the application of gene technology such as Cuba and China. While the developing countries are struggling to improve their basic health care, research on gene technology in the western countries proceeds fast. The early identification of a particular gene constitution will show whether a young adult is at higher risk of important diseases such as various forms of cancer, cardiovascular disease, diabetes or psychiatric disorders. The therapeutical, preventive, psychological and some ethical aspects of this new era of predictive medicine will be discussed.