Semantic interoperability (SIOp) is a major issue for health care systems having to share information across professionals, teams, legacies, countries, languages and citizens. The World Health Organisation (WHO) develops and updates a family of health care terminologies (ICD, ICF, ICHI and ICPS) and has embarked on an open web-based cooperation to revise ICD 11 using ontology driven tools. The International Health Terminology Standard Development Organisation (IHTSDO) updates, translates and maps SNOMED CT to ICD 10. We present the application of the CEN/ISO standard on categorial structure to bind terminologies and ontologies to harmonise and to map between these international terminologies.