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Unified Medical Language System® (UMLS®)

The Metathesaurus

Over 100 vocabularies, code sets, and thesauri, or "source vocabularies"are brought together to create the Metathesaurus. Terms from each source vocabulary are organized by meaning and assigned a concept unique identifier (CUI).

Sixty-two percent of the Metathesaurus source vocabularies are in English. However, the Metathesaurus also contains terms from seventeen other languagessuch as Spanish, French, Dutch, Italian, Japanese, and Portuguese.

The table below shows some of the terms that are part of the concept "Atrial Fibrillation." The source vocabulary that contributed each term is listed after it. Often a source vocabulary will contribute more than one term to a concept.

TermSource Vocabulary
Atrial fibrillation ICD-9-CM
AF NCI Thesaurus
Atrial fibrillation (disorder) SNOMED Clinical Terms
atrium; fibrillation ICPC2-ICD10 Thesaurus


The UMLSMetathesaurus organizes all of the original data from the source vocabulary including unique identifiers, definitions, or term spelling variants into a common format.

Last Reviewed: July 29, 2016