What is the relationship among the following article reference numbers: PMCID, NIHMSID, and PMID? The PMCID is a unique reference number or identifier that is assigned to every article that is accepted into PMC. The PMCID is also used by recipients of NIH funding to demonstrate compliance with the NIH Public Access policy. The PMCID can be found in both PMC and PubMed. The NIHMSID is a preliminary article identifier that applies only to manuscripts deposited through the NIHMS system. The NIHMSID is only valid for compliance reporting for 90 days after the publication date of an article. Once the Web version of the NIHMS submission is approved for inclusion in PMC and the corresponding citation is in PubMed, the article will also be assigned a PMCID. The PMID is a unique reference number for PubMed citations. The PMID is a distinctly different number from the PMCID and is used only for PubMed records.