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NLM Classification 2015: Worldwide source of medical library classification

About the NLM Classification

Scope of Revision
Historical Development
Structure of the NLM Classification
Relationship to MeSH®

Scope of Revision

This edition incorporates all 2015 additions and changes to the schedules (see Class Numbers Added and Canceled) and to the index, which has been newly edited and updated with appropriate MeSH concepts. One hundred and thirty-one (131) new index entries were created of which twenty-three (23) are from the 2015 MeSH; the remainder are MeSH terms from previous years. Numerous main index entries and cross references were modified to reflect changes in the MeSH vocabulary. Forty-three (43) index entries were deleted.

Although the broad nature of the NLM Classification schedules precludes complete correspondence with MeSH, new class numbers were added and existing class numbers were canceled as needed to reflect other changes in MeSH and the biomedical and related sciences literature cataloged.

The WE (Musculoskeletal System) and WG (Cardiovascular System) schedules were the major area of focus for the 2015 edition.

Changes were made to the WE schedule outline headers:

  • WE 168-190 Orthopedics. Reconstructive Orthopedics. Bone Transplantation was changed to Orthopedic Procedures.
  • WE 300-400 Joint Tissues was changed to Joint and Connective Tissues.
  • WE 700-715 Head and Trunk was changed to WE 700-708 Head and Neck.
  • WE 710-760 Torso was added.
  • WE 720-755 Back was deleted.

Some WE and WG class number captions and notes were revised to better reflect the scope of the number. For example:

  • At WE 21, the caption was changed from Orthopedics as a profession. Osteology as a profession. Ethics. Peer review to Orthopedics, osteology or rheumatology as a profession. Ethics. Peer review.
  • At WE 103, the caption was changed from Physical exertion to Movement. Locomotion.
  • At WE 104, the caption was changed from Kinesthesis. Weight perception to Proprioception. Psychomotor performance.
  • At WE 170, the note was added: Classify here all works on amputation regardless of site.
  • At WE 172, the caption was changed from Prosthesis. Prosthesis implantation (General) to Artificial limbs.
  • At WE 400, the caption was changed from Bursae to Synovial bursa. Bursitis.
  • At WE 544, the caption was changed from Myositis. Fibrositis. Rheumatism to Rheumatic diseases.
  • At WE 700, the caption was changed from Head and trunk to Head and neck.
  • At WE 835, the caption was changed from Fingers. Toes to Fingers.
  • At WE 880, the caption was changed from Ankle. Foot to Ankle. Foot. Toes.
  • At WG 202, the caption was changed from Physiology. Heart beat mechanism to Physiology.
  • At WG 205, the caption was changed from Cardiac emergencies to Cardiac emergency treatment.
  • At WG 320, the caption was changed from Functional heart disease to Neurocirculatory asthenia.
  • At WG 330, the caption was changed from Disorders of the heart beat to Cardiac arrhythmias (General).

Changes were made to other class schedules. For example:

  • At W 323, the caption was changed from Medical missions to Missions. Missionaries. The note was revised to: Classify biographical or autobiographical works of medical missionary doctors and nurses in WZ 100.
  • At WP 155, the note was added: Classify works on the pelvic bones in WE 760.
  • At WQ 202, the caption was changed from Diagnosis to Pregnancy determination.
  • At WQ 225, the caption was changed from Spontaneous abortion. Fetal death to Spontaneous abortion. Fetal death. Perinatal death.

A change was made to Table G (Geographic Notations).

  • One Table G number caption was modified: GS3.Scandinavia was changed to Scandinavia and Nordic Countries.

Historical Development

The genesis of the NLM Classification is a Survey Report on the Army Medical Library, published in 1944, which recommended that the "Library be reclassified according to a modern scheme," and that the new scheme be a mixed notation (letters and numbers) resembling that of the Library of Congress. Subsequently a classification committee was formed, chaired by Keyes D. Metcalf and including Mary Louise Marshall who compiled the schedules. Medical specialists acted as consultants to the committee. Based on the consultants' advice, that of the committee and of the NLM cataloging staff, Ms. Marshall produced a preliminary edition of the Library's Classification, which was issued in 1948.

The preliminary edition was revised by Frank B. Rogers and the first edition of the new classification was published in 1951 as the U.S. Army Medical Library Classification. It firmly established the current structure of the classification and NLM's classification practices. The headings for the individual schedules were given in brief form (e.g., WE - Musculoskeletal System; WG - Cardiovascular System) and together they provided an outline of the subjects that constitute the National Library of Medicine Classification . These headings were interpreted broadly as including the physiological system, the specialty or specialties connected with them, the regions of the body chiefly concerned and subordinate related fields. Within each schedule, division by organ usually has priority. All schedules, including some of their sections, are preceded by a group of form numbers representing publication types. These numbers, ranging generally from 1-39, are employed as mnemonic devices throughout the Classification.

Beginning with the 2002 edition, the National Library of Medicine Classification is published in electronic form and updated annually:

The online environment offers many advantages to users including hyperlinks between class numbers in the index and the schedules, and between terms within the index and direct links from these to the MeSH record itself under the MeSH Browser.

The online data creation and maintenance system of the Classification gives NLM the ability to update the classification annually in tandem with MeSH. Publication of printed editions ceased with the 5th revised edition, 1999. Beginning with the 2006 edition, the NLM Classification is also available in PDF (Portable Document Format) at

Structure of the NLM Classification

The National Library of Medicine Classification covers the field of medicine and related sciences, utilizing schedules QS-QZ and W-WZ, permanently excluded from the Library of Congress (LC) Classification schedules. The various schedules of the LC Classification supplement the NLM Classification for subjects bordering on medicine and for general reference materials. The LC schedules for Human Anatomy (QM), Microbiology (QR) and Medicine (R) are not used at all by the National Library of Medicine since they overlap the NLM Classification.

Relationship to MeSH

The schedules, with their special requirements for use with all types and forms of materials, preclude strict adherence to the hierarchical arrangement of the Medical Subject Headings (MeSH), the Library's thesaurus for indexing and cataloging. The schedules maintain their own character in order to provide for material, old as well as new, acquired for the Collection, including dictionaries, atlases, directories and other items, which are not suitable for the arrangements, found in MeSH. However, an effort was made to make schedule headings, subheadings and class number captions compatible with MeSH terminology. The MeSH Tree Structures were used extensively to determine the proper placement of a concept in a schedule and to relate index headings to one another. Since the representation of subjects in the schedules of the NLM Classification is intentionally broad, the captions do not enumerate all of the subordinate concepts that are to be classified in a given number. MeSH descriptors for these subordinate concepts do appear in the index, to the extent practical with appropriate references to the classification numbers.


The Index to the NLM Classification consists primarily of Medical Subject Heading (MeSH) concepts used in cataloging. It includes concepts first appearing in the latest edition of MeSH and other older concepts as warranted by the literature cataloged. It also provides access to classification numbers through these MeSH concepts. Index entries are updated annually to reflect additions and changes of the latest edition of MeSH. For additional information on the Index see About the Index.