This resource was designed during a PhD in medical informatics (funded by INSERM, 2010-2012). Its components are (i) a core ontology consistent with a metamodel (disorders and groups of disorders, genes, clinical signs and their relations) and (ii) an instantiation of this metamodel with Orphanet Data (available on http://orphadata.org). </ br> Research experiments demonstrated (i) efficient classifications generation based on SPARQL Construct, (ii) perspectives in semantic audit of a knowledge base, (iii) semantic comparison with OMIM (www.omim.org) using proximity measurements and (iv) opened perspectives in knowledge sharing (LORD, http://lord.bndmr.fr). Current production services of Orphanet developed ORDO, released in 2014, an ontology synchronized with their production database. This ontology is now available on Bioportal.