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MeSH Trees, 2012. Documentation and Availability

1. MeSH Trees

The National Library of Medicine makes a hierarchical arrangement of its Medical Subject Headings (MeSH) with their associated tree numbers available in an electronic file.

These hierarchical data are collectively known as the MeSH Tree Structures. They are updated annually and users of the data are encouraged to obtain the new year's data each year.

The MeSH Tree Structures data are only a part of NLM's MeSH data. They do not include, for example, cross-references, scope notes, or subheadings. These data are available as MeSH in MARC format, and ASCII MeSH. ASCII MeSH also contains Supplementary Concept Records (formerly Supplementary Chemical Records). Also, two Descriptors do not have Tree Numbers: "Male" and "Female".

2. Restrictions on use

No license is required, however, use of the trees file data is subject to conditions which are detailed in the Memorandum of Understanding.

3. Availability

MeSH Descriptors and Qualifiers are also published annually in a printed version, including MeSH Trees.

MeSH Trees are available online in PDF and HTML format.

4. File format

The file contains essentially the same data as the online MeSH Tree Structures - one entry for each MeSH tree number and the corresponding heading, and the entries are ordered by tree number. For example,


Unlike the numbers in the online Trees, every node contains three characters, e.g., A01 instead of A1. The heading is separated from the tree number by a semi-colon.

Note that because a MeSH main heading may have more than one tree number, the number of entries is much greater than the number of headings.

The file is in ASCII format, with entries separated by a carriage return and line feed.

5. File contents - 2012 MeSH

There are 54,091 entries, one for each tree number in 2012 MeSH, which contains 26,581 main headings. The file is 2.1MB in size (2,162,761 bytes).

6. Contacts

For questions concerning the content of the MeSH Tree Structures, contact:

Stuart Nelson, M.D.
Head, Medical Subject Headings
National Library of Medicine
6701 Democracy Blvd, Suite 202
Bethesda, MD 20894

voice: 301-496-1495; FAX: 301-402-2002

For questions concerning distribution, format, etc., contact:

Jacque-Lynne Schulman
Medical Subject Headings
voice: 301-496-1495; FAX: 301-402-2002