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Question: Why am I retrieving MEDLINE (rather than OLDMEDLINE) citations with publication dates prior to 1966?


MEDLINE includes records citing articles published prior to 1966 (about 2.1 million).

As of late 2006, the set of records marked with a status of MEDLINE includes OLDMEDLINE records where all of the original subjects have been mapped to current MeSH vocabulary. These OLDMEDLINE records will be retrieved in PubMed when limiting to the MEDLINE® subset by searching medline [sb].

In the fall of 2015, NLM processed all OLDMEDLINE citations using a form of the Medical Text Indexer software modified specifically for this subset of MEDLINE data in order to add additional MeSH Headings and complete a project that mapped OLDMEDLINE Other Term (OT) subject headings to MeSH Headings. The result of this project was that, as of December 2015, all OLDMEDLINE citations now have at least one MeSH Heading and were, therefore, converted to MEDLINE status.

PubMed searchers not interested in these older citations are advised to restrict their searches using the date range function within the Limits feature, or to set up a filter for publication date.

Searchers can isolate records that originated from the older print indices of the Cumulated Index Medicus (CIM) and the Current List of Medical Literature (CLML) by searching the value jsubsetom.

See also the Technical Bulletin articles Changes to OLDMEDLINE Records - Status Tag Change (, and MEDLINE Data Changes - 2016 (

For more information on:


MEDLINE Fact Sheet

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