Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

MEDLINE Indexing Online Training Course

MeSH Headings & Trees

Hierarchical Structure

Each MeSH term is located in one or more trees. The tree structure goes from more general terms to more specific terms. It is important that indexers use the trees to find the most specific term applicable. Each MeSH record contains the portion of the Tree(s) showing its location. Below is an example of the Tree location for MeSH term PERITONEUM:

MeSH tree for Peritoneum

The MeSH trees are very important to the indexing process, and indexers should routinely use them.

  1. Indexers should always "scroll down" the tree in the MeSH browser to see if a more specific term than the one they chose is available.
  2. Indexers should use the tree to group MeSH terms. If the article discusses several similar concepts (diseases, drugs, techniques, etc), they can be grouped under the next more general term determined by the tree structure. Use the Rule of Three below to determine which term to index.
  3. Indexers should view the tree where a specific MeSH term is located to help determine the slant of the article and the choice of subheadings for supporting MeSH terms. For example the term COMPLEMENT ACTIVATION is located under IMMUNE SYSTEM PROCESSES [G12.425 tree]. Thus the slant of an article where complement activation is the main point would be immunologic. The subheading /immunology would be used on the appropriate organ, organism or disease term where complement activation is tasking place.

    Complement activation in patients with rheumatoid arthritis
    HUMAN (check tag)

Last Reviewed: January 24, 2017