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Unified Medical Language System® (UMLS®)

Unified Medical Language System (UMLS)

The UMLS integrates and distributes key terminology, classification and coding standards, and associated resources to promote creation of more effective and interoperable biomedical information systems and services, including electronic health records.

Access the UMLS

Sign up for a license, download files, and browse UMLS data

What is the UMLS?

The UMLS, or Unified Medical Language System, is a set of files and software that brings together many health and biomedical vocabularies and standards to enable interoperability between computer systems.

Get Started

Request a license and sign up for a UMLS Terminology Services (UTS) account.

  • UMLS licenses are issued only to individuals and not to groups or organizations.
  • There is no charge for licensing the UMLS from NLM. NLM is a member of SNOMED International (owner of SNOMED CT), and there is no charge for SNOMED CT use in the United States and other member countries. Some uses of the UMLS may require additional agreements with individual terminology vendors.
  • The UTS account allows you to browse, download, and query the UMLS.
  • For more, visit how to license and access UMLS data

UMLS in Use

You can use the UMLS to:

  • Link terms and codes between your doctor, your pharmacy, and your insurance company
  • Coordinate patient care among several departments within a hospital
  • Process texts to extract concepts, relationships, or knowledge
  • Facilitate mapping between terminologies
  • Develop an information retrieval system
  • Extract specific terminologies from the Metathesaurus
  • Create and maintain a local terminology
  • Develop a terminology service
  • Research terminologies or ontologies

The Three UMLS Knowledge Sources

  • Metathesaurus: Terms and codes from many vocabularies, including CPT, ICD-10-CM, LOINC, MeSH, RxNorm, and SNOMED CT. Hierarchies, definitions, and other relationships and attributes.
  • Semantic Network: Broad categories (semantic types) and their relationships (semantic relations).
  • SPECIALIST Lexicon and Lexical Tools: A large syntactic lexicon of biomedical and general English and tools for normalizing strings, generating lexical variants, and creating indexes.

Accessing the UMLS

The UMLS Terminology Services (UTS) provides three ways to access the UMLS:

Web Browsers

You can search the data through UTS applications:

Local Installation

To install the UMLS on your computer, download the files. The MetamorphoSys tool, included with the downloaded files, allows you to customize the UMLS according to your needs. You can then load your customized data into your own database system, such as MySQL or Oracle, or you may browse your data using the MetamorphoSys RRF browser.

Web Services APIs

You can use our APIs to query the UMLS data within your own application.

Citing the UMLS

If you use the UMLS data and tools in your work, please cite:

UMLS Knowledge Sources [dataset on the Internet]. Release 2024AA. Bethesda (MD): National Library of Medicine (US); 2024 May 6 [cited 2024 Jul 15]. Available from:

If you reference the UMLS project in your article, please cite:

Bodenreider O. The Unified Medical Language System (UMLS): integrating biomedical terminology. Nucleic Acids Res. 2004 Jan 1;32(Database issue):D267-70. doi: 10.1093/nar/gkh061. PubMed PMID: 14681409; PubMed Central PMCID: PMC308795.

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Last Reviewed: March 10, 2021