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Introduction to the Unified Medical Language System

The Unified Medical Language System (UMLS) is a set of files and software available from the U.S. National Library of Medicine (NLM) that brings together many biomedical vocabularies and standards for drugs, disorders, procedures, lab tests, medical devices, organisms, anatomy, genes, and more.

As part of the series, Clinical Information, Librarians and the NLM: from Health Data Standards to Better Health, David Anderson from the NLM explains how researchers and organizations can use the rich collection of terminology data in the UMLS to enhance interoperability and discoverability in research and clinical applications..

Webinar materials:

Webinar Q&A:

Q: Could you speak to selection process for new terminologies added to the UMLS?

A: You can find a set of criteria for inclusion in the UMLS at:

Q: Is the UMLS continuously updated?

The UMLS brings in new content on a regular basis, and we release the UMLS twice a year in May and November. We update around 25 terminologies plus translations per 6 month release cycle. For a list of terminologies in the UMLS, see:

Q: How synonymy is established?

Algorithms help assign names to concepts. Editors who work on the UMLS review all new content and make final decisions on synonymy.

Q: How does the UMLS deal with terminologies that may have conflicting hierarchies?

A: We represent hierarchies exactly they are represented in the source terminologies. We do not edit them. In some cases, they may conflict. For more information about hierarchies in the UMLS, see:

Q: Are there any possibilities for group licenses in the future?

A: This would be really nice, but at present we have no plans for group licenses. We license to individuals only. See the Licensing/Requirements section of our FAQ:

Q: How do we as librarians help our patrons use this?

Q: Would you suggest some effective ways to start a conversation with researchers about why they may want to incorporate UMLS into their research?

A: UMLS is primarily a research tool. Get to know the body of research where UMLS has been utilized: Are your patrons engaging in similar research? If they are, then the UMLS and its associated tools may be of use to them. Keep in mind that the UMLS has a steep learning curve and requires a very specific skillset.


Last Reviewed: November 25, 2019