[Surveillance of rare diseases in Spain: Spanish Registry of Rare Diseases (ReeR).]

Traditionally, epidemiological surveillance has focused on infectious diseases, but the concept of Public Health surveillance, introduced in Spain with the Law 33/2011, is broader and includes chronic diseases. Health strategies for these diseases need epidemiological information to improve understanding of socio-health needs and to facilitate the efficient management of resources. The European Union defines rare diseases (RD) as those that, being life-threatening or chronically debilitating, have a prevalence of less than 5 cases per 10,000 inhabitants. The RD Strategy of the National Health System, approved in 2009 and updated in 2014, recommends the development of regional registries of rare diseases (RAER), in addition to a national registry. The REpIER and Spain-RDR projects of the Institute of Health Carlos III (ISCIII) promoted the creation and regulation of 94% of the RAER. After more than 10 years of initiatives and work to improve the knowledge of RD's epidemiology in Spain, it was possible to implement the Spanish Registry of Rare Diseases (ReeR) in 2015, becoming one of the first population surveillance systems for chronic diseases of state scope. The ReeR procedures manual is the result of consensus between the RAER, the Ministry of Health, the ISCIII and the patient associations. The participatory methodology used for the implementation and launching of ReeR is considered an added value. The information system implemented will allow improving knowledge about the prevalence and distribution of RD in Spain.