The rare diseases are a group of diseases which diagnosis, treatement and prevention is a relevant problem all over the world. They are defined on the basis of their very low incidence also if this definition is not equal all over the world. The article offers a review of the national and regional legislation on rare diseases and it describes a survey carried out in Fondazione Ospedale Maggiore Policlinico IRCCS Mangiagalli Regina Elena, a research and teaching hospital, about the organization of the network of doctors who care for these patients.