The UMLS Semantic Network is one of three UMLS Knowledge Sources developed as part of the Unified Medical Language System project. The network provides a consistent categorization of all concepts represented in the UMLS Metathesaurus.

Semantic Network

The Semantic Network consists of (1) a set of broad subject categories, or Semantic Types, that provide a consistent categorization of all concepts represented in the UMLS Metathesaurus, and (2) a set of useful and important relationships, or Semantic Relations, that exist between Semantic Types. This section of the documentation provides an overview of the Semantic Network, and describes the files of the Semantic Network. Sample records illustrate structure and content of these files.

Further information about the UMLS Semantic Network can be found at:

Semantic Network Fact Sheet UMLS Semantic Network Fact Sheet
Semantic Network Documentation UMLS Semantic Network Documentation
Comp Funct Genom 2003; 4:80-4 McCray AT. An upper level ontology for the biomedical domain. Comp Funct Genom 2003; 4:80-4.

The UMLS Semantic Network is available in unit record and relational format and is distributed subject to these terms and conditions.
Download the files

Semantic Groups

The UMLS semantic network reduces the complexity of the Metathesaurus by grouping concepts according to the semantic types that have been assigned to them. For certain purposes, however, an even smaller and coarser-grained set of semantic type groupings may be desirable. The following principles were used to design the groupings: semantic validity, parsimony, completeness, exclusivity, naturalness, and utility. The semantic groups provide a partition of the UMLS Metathesaurus for 99.5% of the concepts.

Further information about the semantic groups can be found at:

Proceedings of Medinfo 2001;10(Pt 1):216-20  McCray AT, Burgun A, Bodenreider O. Aggregating UMLS semantic types for reducing conceptual complexity. Proceedings of Medinfo 2001;10(Pt 1):216-20.
Journal of Biomedical Informatics 2003;36(6):414-432  Bodenreider O, McCray AT Exploring semantic groups through visual approaches. Journal of Biomedical Informatics 2003;36(6):414-432.

The UMLS semantic groups are made available through a file called SemGroups.txt. There is one line in this file for each semantic type. The identifier and the name of the semantic group are repeated for each semantic type included in the group, before the identifier (TUI) and the name (STY) of the semantic type.


The Semantic Network Files Download the current UMLS Semantic Network files (tzg compressed file)
The Semantic Network Files Download the current UMLS Semantic Group file (bar-delimited text file)

An archive of past versions of the Semantic Network and Semantic Group files is available here. The companion table lists the number of semantic types and relations for each version since 1990.


Email: Olivier Bodenreider