Skip Navigation Bar
National Library of Medicine Technical BulletinNational Library of Medicine Technical Bulletin

Table of Contents: 2023 NOVEMBER–DECEMBER No. 455

Previous Next

UMLS® 2023AB Release Available

UMLS® 2023AB Release Available. NLM Tech Bull. 2023 Nov-Dec;(455):e1.

2023 November 06 [posted]

The 2023AB release of the Unified Medical Language System® (UMLS) Knowledge Sources is available for download as of November 6, 2023.

The available downloads are:

  • UMLS Metathesaurus Precomputed Subsets (Requires no installation, see below for more information.)
  • MRCONSO.RRF file (Most widely used Metathesaurus file.)
  • Full Release (UMLS Metathesaurus, Semantic Network, Specialist Lexicon and Lexical Tools, database load scripts, and MetamorphoSys for customizing your UMLS subset and browsing the data.)
  • UMLS Metathesaurus History Files (Files that contain historical data from the UMLS Metathesaurus.)

UMLS Metathesaurus Precomputed Subsets

In past years, we have required the use of MetamorphoSys to install and customize the UMLS Metathesaurus. Now we are providing two ready-to-use precomputed subsets of the UMLS Metathesaurus that require no installation or customization.

  • UMLS Metathesaurus Full Subset (Complete Metathesaurus data without any customization.)
  • UMLS Metathesaurus Level 0 Subset (Includes only level 0 source vocabularies. Level 0 vocabularies do not have any additional restrictions beyond the standard license terms.)

UMLS Metathesaurus History Files

  • Concept History (MRCONSO_HISTORY.txt) - This file contains all atoms, concepts, and codes that were dropped from the UMLS Metathesaurus MRCONSO.RRF starting with the 2004AA release.
  • Relation History (MRREL_HISTORY.txt) - This file contains all relations dropped from the UMLS Metathesaurus MRREL.RRF file starting with the 2004AA release.
  • Source Vocabulary History (MRSAB_HISTORY.txt) - This file includes a row for every version of every UMLS source vocabulary updated in the UMLS Metathesaurus MRSAB.RRF file starting with the 2004AA release.

These files are available from the UMLS Download page:

Please let us know if you find these files useful with comments to the NLM Help Desk ( using the subject line: "UMLS History Files."


The 2023AB Metathesaurus contains approximately 3.36 million concepts and 15.9 million unique concept names from 185 source vocabularies.

32 English sources and 38 translation sources were updated. These include MeSH®, MedDRA, RxNorm, and SNOMED CT® (English and Spanish). For detailed information on changes in this version of the Metathesaurus, see the Updated Sources (Expanded) section. Additional release statistics may be found in the Statistics section.


  • The full release requires 34.2 GB of disk space.

Reported bugs may be viewed on the Release Notes and Bugs webpage.

MetamorphoSys can generate custom load scripts for MySQL, Oracle, or Microsoft Access when creating a Metathesaurus subset or installing the Semantic Network. Instructions are available on the UMLS Load Scripts homepage.

Release Information

To access the UMLS Release files, you must have an active UMLS Metathesaurus® License and a valid UTS account. You will be prompted to authenticate with an identity provider with the UTS when downloading the files.

UMLS Learning Resources

2023AB Source Release Documentation webpages are available. 

Additional information regarding the UMLS is available on the UMLS homepage. New users are encouraged to take the UMLS Basics Tutorial and to explore the UMLS Quick Start Guide, and other training materials.

UMLS Terminology Services (UTS)

The UTS Metathesaurus Browser and the UTS REST API include the updated release.


UMLS REST API authentication has changed. You can now authenticate by simply appending an apiKey parameter to your request, for example:{{YOUR_API_KEY}}. 

Authentication via ticket-granting tickets (TGTs) and service tickets is deprecated, but we will continue to accept API authentication via this method until the end of 2023.

UMLS API Search Endpoint:

  • Partial matches: On December 22, 2022, we added a parameter to the search endpoint that returns partial matches. Adding partialSearch=true to your search query will return results that match at least one word in your query. Documentation:
  • Stemming: On July 17, 2023, we made some changes to the way in which the UMLS API search endpoint handles stemming of individual words. The most significant impact is that queries that include plural forms of words will now find singular forms, for example, a query for "lungs" will find all instances of "lung." In general, API search queries and search queries in the Metathesaurus Browser will produce a higher number of results than before.

Validating API Keys: We are now offering an API endpoint for validating API keys. This is useful for application developers who need to ensure that their users are UMLS licensees. Make a request that includes both your API key (validatorApiKey) and the API key of the user of your application (apiKey).

For example:

Deprecated Subsets and Content Views API Endpoints are shutting down as of December 31, 2023: These endpoints were deprecated in May of 2022. Source-Asserted Subset information and Content View information can be retrieved from the UMLS Metathesaurus files.

UMLS User Contributions

UMLS users have extended the functionality of the UMLS in a variety of ways by developing APIs, automation scripts, and natural language processing tools. You can find a list of these on the UMLS Community webpage:

Want to add your tool? Send a request to the NLM Help Desk ( with the subject line: "UMLS Community."

Be sure to include a link to your source code so that other UMLS users can adapt your tool. We are especially interested in:

  • Database load scripts.
  • Transformation scripts that convert UMLS data into other formats (for example, RDF or JSON).
  • Scripts that automate any aspect of UMLS installation.
  • Applications that leverage UMLS in the processing of text.

We value your feedback! For more information about improvements we have made to the UMLS based on user feedback, as well as information about UMLS use in general, see our UMLS User Feedback Page:

NLM Technical Bulletin National Library of Medicine National Institutes of Health