The concept "inborn error of metabolism" (IEM) arose from the observations of Sir A. Garrod at the beginning of the XXth century. The exponential development, during the last decades, of our knowledge in cellular biology and molecular genetics, and the availability of increasingly more precise diagnostic tools, allow the identification of a still growing number of inborn errors of metabolism. Their physiopathology is better understood. Treatments have considerably improved: more specific diets, new medical treatments, enzyme replacement therapy, organ transplantation, hepatocyte or stem cell transplantation... New techniques are under development, including various strategies of gene therapy. Improved therapeutic efficacy combined with earlier diagnosis have dramatically changed the prognosis of many disorders. As a consequence, new challenging questions have to be answered. Today, patients with an IEM, because of the extreme complexity of their management, need to be looked after by a multidisciplinary team of physicians (pediatricians and internists), dieticians, social workers, psychologists... It is essential, in this complex and rapidly expanding field, that experiences should be shared at national and international level, in order to provide the most adequate care for patients.