Skip Navigation Bar

Fact Sheet
UMLS® Terminology Services


The UMLS Terminology Services (UTS) provides online access to the Unified Medical Language System® (UMLS®) Knowledge Sources and other National Library of Medicine (NLM) terminology resources. The UTS allows single sign-on access to all UMLS resources: Web-based terminology browsers, file downloads, reporting tools, and user profile management.

The UTS Applications menu includes browsers for the Metathesaurus, the Semantic Network and SNOMED CT®. The Metathesaurus and SNOMED CT browsers have terminology and code searching capabilities as well as tree browsers for exploring the hierarchical structure of source vocabularies within the UMLS. The Semantic Network browser allows you to browse the terms, relations and hierarchy of the Semantic Network.

You must have an active UMLS Metathesaurus License to access the UTS. For instructions on requesting a license and accessing the UTS, see How to License and Access the Unified Medical Language System® (UMLS®) Data.

Metathesaurus® Browser

The Metathesaurus Search tab allows you to search the Metathesaurus by term, concept unique identifier (CUI), or code. You can query data from Metathesaurus concepts, such as definitions, semantic types, related concepts, hierarchical details, and co-occurrence information. You can restrict your search to a particular source vocabulary.

The Metathesaurus Tree tab allows you to navigate the hierarchy of a selected source vocabulary to browse both its content and structure. Note: The Metathesaurus Tree Browser includes only those source vocabularies that have a hierarchical structure.

Semantic Network Browser

The Semantic Network List tab allows you to browse the Semantic Network for specific semantic types and semantic relations. You can query the Semantic Network to learn the semantic relations existing between semantic types.

The Semantic Network Tree tab shows the hierarchical representation of the semantic types and semantic relations that comprise the Semantic Network.

SNOMED CT® Browser

The SNOMED CT Search tab enables you to browse SNOMED CT concepts that are present in the Metathesaurus. You may search by term, SNOMED CT ConceptID, or SNOMED CT DescriptionID.

The SNOMED CT Tree tab allows you to browse the SNOMED CT Top Level Concept codes and their children.

Note that the UMLS Metathesaurus may not include the latest version of SNOMED CT.

SPECIALIST Lexicon and Lexical Tools

You can access SPECIALIST Natural Language Processing (NLP) Tools through the Resources menu of the UTS.


The Downloads menu of the UTS provides access to several NLM terminology resources, including the UMLS Knowledge Source files, RxNorm files, and SNOMED CT files.

Developer Resources

The UTS is also the source for Application Programmer Interfaces (APIs). These are for users who wish to query and retrieve data remotely from the UMLS within their own applications. You can find API documentation under the Documentation menu of the UTS.

The UTS includes the RESTful API that allows authorized content distributors to verify that their third-party users have an active UMLS license. You can find documentation for Validating UMLS Licensees under the Documentation menu of the UTS. 


Other Fact Sheets in the UMLS series: UMLS Metathesaurus, UMLS MetamorphoSys, UMLS Semantic Network, SPECIALIST Lexicon, and Unified Medical Language System (UMLS).

For general information on NLM services, contact:

National Library of Medicine
Customer Service
8600 Rockville Pike
Bethesda, MD 20894
Telephone: 1-888-FINDNLM (1-888-346-3656)
NLM Customer Service Form at

A complete list of NLM Factsheets is available at:
(alphabetical list):
(subject list):

Or write to:

Office of Communications and Public Liaison
National Library of Medicine
8600 Rockville Pike
Bethesda, MD 20894

Phone: (301) 496-6308
Fax: (301) 496-4450