Clinical genetics has reached a crossroads. Indeed recent progress in molecular genetics has generated great hope. This progress has consequences beyond genetic diseases, leading to the understanding of much more general mechanisms of disease. This progress has also permitted a better classification of genetic entities, such as Alport's syndrome, based on the molecular mechanisms involved. Lastly this progress allows us to design pharmacologic therapeutic approaches. Enzyme replacement therapy in Fabry's disease is a recent example of this approach. Difficulties are much greater in diseases such as autosomal dominant polycystic kidney disease. To reach these goals, height collaboration between molecular genetics and cell biology in the post-gene era, and between clinical genetics and other medical specialties, is required not only in the field of pediatric diseases, but also in late-onset genetic diseases.