42 CFR §424.506

1. (a)Definition. Eligible professional means any of the professionals specified in section 1848(k)(3)(B) of the Act.
2. (b)Enrollment requirements.
   1. (1)A provider or a supplier that is eligible for an NPI must do the following:
      1. (i)Report its NPI on its Medicare enrollment application.
      2. (ii)If the provider or supplier was in the Medicare program before obtaining an NPI and the provider's or the supplier's NPI is not in the provider's or supplier's Medicare enrollment record, the provider or supplier must update its Medicare enrollment record by submitting its NPI using either of the following:
         1. (A)The applicable paper CMS-855 form.
         2. (B)Internet-based PECOS.
   2. (2)A physician or eligible professional who has validly opted-out of the Medicare program is not required to submit a Medicare enrollment application for any reason, including to order or certify.
3. (c)Claims reporting requirements.
   1. (1)A provider or supplier that is enrolled in Medicare and submits a paper or an electronic claim must include its NPI and the NPI(s) of any other provider(s) or supplier(s) identified on the claim.
   2. (2)A Medicare beneficiary who submits a claim for service to Medicare—
      1. (i)Must include the legal name of any provider or supplier who is required to be identified in that claim; and
      2. (ii)May, if known to the beneficiary, include the National Provider Identifier (NPI) of any provider or supplier who is required to be identified in that claim.
   3. (3)A Medicare contractor will reject a claim from a provider or a supplier if the required NPI(s) is not reported.