UMLS, or Unified Medical Language System

UMLS – Quick start guide

What is the UMLS?

The UMLS, or Unified Medical Language System, is a collection of files and software that brings together many biomedical vocabularies and standards to enable interoperability between computer systems. It is developed by the National Library of Medicine of the USA.

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

The SNOMED dictionary in Spanish can be easily integrated into OPENEMR to standardize medical terminology in our language.

Use of the UMLS

A powerful use of UMLS is the linking of medical information, medical terms, names of medicines and billing codes through different computer systems. Some examples of this are:

• Linkage of terms and codes between your doctor, your pharmacy and your insurance company
• The coordination of patient care among several departments of a hospital

The UMLS has many other uses, including data recovery in search engines, data mining, public health reports, statistics and terminology research.

The three UMLS tools

The UMLS has three tools, what we call the Sources of Knowledge:

• Metathesaurus: Terms and codes of many vocabularies, including CPT®, ICD-10-CM, LOINC®, MeSH®, RxNorm and SNOMED CT®
• Semantic Network: general categories (semantic types) and their relationships (semantic relationships)
• Specialized lexicon and lexical tools: natural language processing tools

We use the Semantic Network and lexical tools to produce the Metathesaurus. The production of Metathesaurus involves:

• Process the terms and codes used by the lexicon tools
• Group synonyms in terms of concepts
• Categorize concepts by semantic types of the Semantic Network
• Incorporate relationships and attributes provided by vocabularies
• Release the data in a common format

Although we integrate these tools for the production of the Metathesaurus, they can be accessed separately or in any combination according to your needs.

More about UMLS tools

Semantic Network
Vocabularies distributed by NLM: MeSH | RxNorm | SNOMED CT

Access the UMLS

UMLS Terminology Services (UTS) provide three ways to access UMLS:

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 – See the names, definitions, and hierarchical structure of the Semantic Network.

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 upload the customized data into your own database system, such as MySQL or Oracle, or you can search your data using the metamorphosys RRF scanner.

Web Services API

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

  • More on Access to the UMLS
  • Terminology Services UMLS
  • Current version
  • Next version
  • Metamorphosys tool
  • API documentation
  • Database loading scripts
  • SQL query diagrams


Apply for a license and register for a UMLS Terminology Services (UTS) account.

• UMLS licenses will be issued only to individuals and not to groups or organizations.
• There is no charge to license the UMLS of the NLM. NLM is a member of the IHTSDO (owner of SNOMED CT), and there is no charge for the use of SNOMED CT in the United States and in other member countries. Some uses of UMLS may require additional agreements with individual terminology providers.
• The UTS account allows you to browse, download and consult the UMLS.