A directory of UPINs was formerly available from the UPIN Registry, as required by Section 4164 of the Consolidated Omnibus Budget Reconciliation Act of 1985, but this service was discontinued after May 23, 2008.
UPINs will be discontinued in the second quarter of 2007 and will replaced by National Provider Identifier, or NPI numbers. There is currently an online NPI look up through the CMS website. https://nppes.cms.hhs.gov/NPPES/NPIRegistryHome.do
— includes a link to detailed information published in the Federal Register