30% of Medicare-enrolled nephrologists were in groups with five or fewer nephrologists in 2024, down from 35% in 2019
Published Jul 2026 · CMS Doctors and Clinicians group rosters and Part B provider types📋 CiteSee the data →
Medicare-enrolled nephrologists by the size of their largest group · 2019–2024
Each clinician is counted once, in the group with the most nephrologists on its roster that year. Bands count nephrologists. Full method below.
Over the same years, the share in organizations of 500 or more physicians rose from 20% to 26%.
The bands. Each year's roster is read on its own and sorted into four bands by the number of nephrologists in the clinician's largest group: five or fewer, 6 to 19, 20 to 49, and 50 or more.
Ownership. Rosters cannot see ownership. A practice owned by a larger company that keeps its own Medicare billing number still counts here as a small group, so a small change does not mean a specialty stayed independent.
A record of group size, not a verdict on whether larger groups are better or worse for patients, prices, or clinicians.
What this is
The share of Medicare-enrolled nephrologists on rosters of each group size, 2019 to 2024.
What it is not
Not a count of acquisitions or mergers, not ownership or employment, and not who bills what. A roster records enrollment, not activity, and cannot show why a group grew.
› How this is counted
Each clinician's specialty is their most frequent Part B provider type across 2020 to 2024, so the 2019 base counts only clinicians who billed in 2020 or later, and clinicians who billed too little Part B to carry a label are not counted. The specialty is Nephrology. Years after 2024 are not included because they are not on the same basis. Each clinician is counted once a year, in the group with the most nephrologists on its roster, and a group that re-registers can appear as a new group. Where a second figure is printed, it counts physicians only, because nurse-practitioner and physician-assistant roster growth moves a count of every clinician. Medicare's 2019 roster snapshot lists fewer clinicians than later years' do, so part of the change since 2019 may reflect a fuller list rather than a shift in group size.