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Unified Medical Language System® (UMLS®)

UMLS - Frequently Asked Questions

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.

You can use the UMLS to enhance or develop applications, such as electronic health records, classification tools, dictionaries and language translators.

Get Started

Begin learning about the UMLS with these tools:

Technical Documentation

The UMLS Reference Manual provides an overview of the UMLS and:

  • Metathesaurus overview and organization (concepts, relationships, attributes)
  • Details about the RRF data files (columns, rows, and descriptions)

Vocabulary Documentation

MetamorphoSys (Local Installation of the UMLS)


UMLS users are encouraged to subscribe to this list, to share their experiences with, or seek advice from the UMLS community on using UMLS resources. NLM also uses this forum to distribute official announcements about UMLS products and services.

  • To subscribe, send an e-mail to: containing the following message: SUBSCRIBE UMLSUSERS-L <your full name>
  • To post a message to the list AFTER subscribing, send an e-mail to:
  • To access subscription information and list archives, go to: UMLSUSERS-L Listserv Web page

The UMLS is updated in May and November of each year. The May release is the AA release (ex. 2015AA) and the November release is the AB Release (ex. 2015AB).

The Release homepage includes release notes, bugs, metadata, and statistics for the latest version of the UMLS.

To view older release notes, go to the Release Documentation Archive.

You must sign up for a license to access the UMLS.

To request a license, click "Sign Up" on the UTS Homepage. Additional information can be found on the UMLS License page.

The UMLS Terminology Services (UTS) provides three ways to access the UMLS. You will need your UMLS username and password to use the UTS.

1) Web Browsers

You can search the data through UTS applications:

  • Metathesaurus Browser - Retrieve UMLS concept information, including CUIs, semantic types, and synonymous terms.
  • Semantic Network Browser - View the names, definitions, and hierarchical structure of the Semantic Network.

2) Local Installation

To install the UMLS on your computer, download the files through the UTS. 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.

3) Web Services APIs

You can use our application programming interfaces (APIs) to query the UMLS data within your own application.

You create a username and password as part of the license application. If you cannot remember your username or password, the UTS Sign In page provides options to retrieve your username and reset your password.

You can search the data through UTS applications:

  • Metathesaurus Browser - Retrieve UMLS concept information, including CUIs, semantic types, and synonymous terms.
  • Semantic Network Browser - View the names, definitions, and hierarchical structure of the Semantic Network.
  • UMLS API - Programmatically search and retrieve UMLS data

You can search the data through your local installation:

  • RRF Browser - Retrieve UMLS concept information, including: CUIs, semantic types, and synonymous terms from your installed data subset.

Go to the Downloads Homepage to view available downloads.

The UMLS Terminology Services (UTS) Web site gives you access to the UMLS browsers, downloads, and APIs.

You can request changes or additions to the UMLS by contacting NLM Customer Support. If additions are specific to the source, you should contact the terminology source provider. Contact information is available in Appendix 1 of the License agreement.

  1. Go to the UTS Sign Up page.
  2. Read and scroll through each tab.
  3. Complete and submit the license form.
  • There are no fees for the UMLS Metathesaurus License
  • Appendix 2 of the license, the SNOMED CT Affiliate License Agreement, refers to fees for the use of SNOMED CT in a non-Member country/territory. Contact SNOMED International with any questions regarding fees for use before signing up for a UMLS license.

Licenses are registered to individuals. There are no organizational or enterprise licenses.

NLM requires at least once licensee per organization. However, it is fine to have multiple licensees from the same organization. Each person who requires access to the browsers and/or downloads must have their own license. We do not encourage users to share account information with one another.

There is not a separate license for commercial organizations. However, if your product incorporates data from the UMLS, you must have a license. Additionally, we require that your clients have a license as well. The same license and rules apply to all users.

Contact the content provider directly to ensure that your use is covered by the UMLS License. Appendix 1 of the license lists contact information for each vocabulary.

As part of the license agreement, you agree to provide NLM with a yearly report of how you used the UMLS. The report is due every January. NLM will send several e-mail reminders in January and you will complete the report through your UTS profile.

As mentioned in the SNOMED CT Affiliate License Agreement, you agree to report to the SNOMED International on your usage of SNOMED CT in non-Member countries. This report is imbedded within the UMLS Annual Report. Complete details are available from SNOMED International.

We welcome any questions and comments via our contact form.

Last Reviewed: December 21, 2017