Who is enrolled in Medicare? The nurse practitioner is now the most common clinician

The Centers for Medicare & Medicaid Services keeps a single master record of everyone approved to bill the program: the Provider Enrollment, Chain and Ownership System, or PECOS. It is the federal system of record that turns an identity — a National Provider Identifier — into billing privileges, under the requirements of 42 CFR Part 424, Subpart P. As of the 2026-05-28 federal release, the enrollment extract holds 2,981,799 active provider-enrollment records, spanning 2,556,656 distinct NPIs across all 50 states, DC, and the territories.

Ask who is in that file and the intuitive answer is "physicians." The data says something more specific — and more consequential for how Medicare actually delivers care.

The most common clinician in Medicare is a nurse practitioner

The single largest provider type in the entire enrollment file is the nurse practitioner: 413,539 enrollment records, or 13.9% of everything in PECOS. That is not the largest physician category — it is the largest category, period. It is ahead of every individual physician specialty by a wide margin.

For comparison, the largest single physician specialty — internal medicine — holds 144,202 enrollment records. There are 2.87 nurse-practitioner enrollments for every internal-medicine enrollment. Family practice, the next physician specialty, holds 129,130. The nurse-practitioner line alone (413,539) is larger than internal medicine and family practice added together (273,332).

The single most common clinician enrolled to bill Medicare is no longer a physician of any specialty. It is a nurse practitioner — and by a wide margin.

One in five enrollments is an NP or a PA

Add the physician assistant — 195,488 records (6.6%) — to the nurse practitioner, and the two advanced-practice categories total 609,027 enrollments, 20.4% of the file. One in five Medicare provider-enrollment records belongs to an NP or a PA.

This is the enrollment-side mirror of a shift CMS's own advisors have tracked on the claims side. MedPAC reports that nurse practitioners and physician assistants now deliver roughly a quarter of all Medicare clinician visits, and that the amount these clinicians bill directly — under their own NPI rather than incident-to a physician — rose sharply over the past five years. The enrollment file is where that shift is registered first: a clinician must be enrolled in PECOS under their own provider type before they can bill under it.

Why the advanced-practice share is so large

Three structural forces sit underneath the number.

Scope-of-practice expansion. Over the past two decades, a growing number of states have granted nurse practitioners full or reduced practice authority — the legal ability to evaluate, diagnose, and prescribe without mandatory physician oversight. Each expansion makes independent Medicare enrollment both possible and worthwhile.

Primary-care economics. Advanced-practice providers are the workforce health systems use to extend access as physician primary-care supply flattens. They train faster and are compensated below physician levels, so a system expanding access into underserved areas enrolls NPs and PAs to do it.

The 85% rule. When a service is billed under an NP's or PA's own NPI, Medicare pays 85% of the physician fee schedule rate; the same service billed incident-to a supervising physician pays 100%. That payment differential is precisely why direct, own-NPI enrollment — the thing PECOS records — has become the policy question MedPAC keeps returning to.

Individuals versus organizations

Most of the file is people. 2,548,303 records (85.5%) carry an individual last name; 433,496 (14.5%) are organizational enrollments carrying an org name instead. The largest organizational provider type is the Part B supplier clinic or group practice — 239,492 records (8.0%), the second-largest category overall behind nurse practitioners. That single fact captures how Medicare is organized today: a vast base of individually-enrolled clinicians, billing through a dense layer of group practices and clinics.

Where providers enroll

Enrollment concentration tracks population and provider supply. California leads with 262,214 records (8.8% of the file), followed by Texas (207,328, 7.0%), New York (198,758, 6.7%), Florida (185,769, 6.2%), and Pennsylvania (127,899, 4.3%). The geography is unremarkable on purpose: enrollment counts scale with the number of providers in a state, so the largest states lead. These are record counts, not per-capita enrollment rates.

What one PECOS record actually is

Each row in the file represents one provider's enrollment to bill Medicare under one provider type. Enrollment is governed by 42 CFR Part 424, Subpart P: a provider or supplier submits a Form CMS-855 application — on paper or through internet-based PECOS — and the Medicare contractor validates eligibility, confirms practice locations and ownership, and grants billing privileges. Because the unit is the enrollment, not the person, a single NPI can appear under more than one provider type or location. That is why the file holds about 1.17 records per distinct NPI, and why every count in this study is reported as enrollment records, not unique individuals.

How this differs from our deactivation study

This study is the composition layer — who is enrolled, and under what provider type. Our companion study, The Medicare deactivation spike: where providers are dropping off, is the churn layer: it tracks providers leaving the enrollment file and where those exits cluster. Read together, they describe both the standing shape of the Medicare provider base and how it turns over. Neither names nor surfaces any individual provider — both are aggregate-only.

Methodology

All counts are direct aggregations over the pecos_providers table, populated from the CMS PECOS Ordering & Referring / provider-enrollment extract (federal release 2026-05-28, 2,981,799 records, RLS Pattern B — public read). Provider-type counts use the CMS-published provider_type_desc field. Individual-versus-organization split uses the presence of an org_name value. State shares use the state_cd field. The exact query is in the reproducibility block below and on the PECOS dataset page; every count resolves to a specific row in a specific frozen federal snapshot. Methodology version: pecos-enrollment/v1.

Limitations

• Snapshot, not a trend. These figures reflect the 2026-05-28 federal release. Enrollment is continuous; counts shift with every monthly refresh.
• Records, not people. Counts are of enrollment records. One NPI can hold several records across provider types or locations, so category totals exceed the number of distinct providers.
• Enrollment, not utilization. A PECOS record is a billing-privilege grant, not a claim. This study measures who is enrolled, not how much each provider billed.
• CMS taxonomy. Provider type is CMS's own enrollment classification (325 categories). It reflects the basis of enrollment, which usually but not always tracks a clinician's day-to-day role.
• Not a quality metric, and aggregate-only. Enrollment counts are a workforce-composition signal, never a measure of care quality. No individual provider is named, surfaced, or attached to any profile in this study.

Sources

• CMS — Provider Enrollment, Chain and Ownership System (PECOS) — the federal enrollment system of record.
• CMS — Ordering & Referring dataset (data.cms.gov) — the public PECOS-derived enrollment extract behind this study.
• 42 U.S.C. — 42 CFR Part 424, Subpart P: Requirements for Establishing and Maintaining Medicare Billing Privileges — the governing enrollment regulation.
• MedPAC — Improving Medicare's payment policies for APRNs and physician assistants — advanced-practice billing growth and the share of Medicare visits.
• CMS — Advanced Practice Non-Physician Practitioners — the 85% physician-fee-schedule payment rule.