Physicians — both MDs and DOs — enroll in Medicare Part B using the same CMS-855I form as other individual providers. Physician enrollment is the foundation of any Medicare billing arrangement: individual physicians, group practices, and hospital-based practices all start with individual physician enrollment.
Individual enrollment
Every physician who wants to bill Medicare must have:
- An active medical license in the state of practice
- A Type 1 NPI (individual)
- Active DEA registration (for prescribing controlled substances)
- Board certification or eligibility in their specialty (some MACs verify this at enrollment)
- Enrollment via CMS-855I or PECOS
Group practice enrollment
If you’re billing through a group practice:
- The group must be enrolled via CMS-855B (if not already enrolled)
- The group must have a Type 2 NPI
- You file CMS-855R to reassign your billing privileges to the group
⚠️ Risk flag: Physicians who join a new group and start billing under that group’s NPI before completing their reassignment are creating improper billing. The effective date of your reassignment matters — CMS can identify and recoup payments made before the reassignment was processed.
Participating vs. non-participating
Participating physicians accept Medicare assignment on all claims. They agree to accept Medicare’s approved amount as payment in full. In return, they’re listed in the Medicare Physician Finder and get their name and address visible to beneficiaries.
Non-participating physicians don’t accept assignment by default but can do so claim-by-claim. They can charge up to 115% of the Medicare approved amount, but beneficiaries pay more out of pocket. This reduces referrals and creates administrative complexity — most physicians participate.
Opt-out: Physicians can opt out of Medicare entirely and enter into private contracts with Medicare beneficiaries. Opt-out requires filing an opt-out affidavit and lasts 2 years. Medicare cannot pay for any services rendered by an opted-out physician, even if the beneficiary pays out of pocket and seeks reimbursement.
Medicare Advantage credentialing
Original Medicare enrollment and Medicare Advantage credentialing are separate processes. Each MA plan has its own credentialing requirements and timelines. Most require:
- Active state license
- DEA certificate
- Board certification
- References and work history
- Malpractice coverage verification
Plan on 60–90 days for MA credentialing in addition to your Medicare enrollment timeline.
Key applications
- CMS-855I — individual physician enrollment
- CMS-855B — group practice enrollment (if you’re forming or joining a group)
- CMS-855R — reassignment of benefits to group
- CMS-460 — Medicare participating physician agreement
- CMS-855O — ordering/referring (usually bundled with 855I enrollment)
Ask Mae if you have questions about participating status, opt-out, or group practice enrollment.