This page compares two distinct NUCC-taxonomy specialties tracked by the CMS National Plan and Provider Enumeration System: Internal Medicine Physician, which currently counts 172,737 enrolled providers across 56 U.S. states and territories, and Nephrology Physician, with 10,569 providers across 55 states. Each clinician on these rosters selected a primary NUCC code at NPI enrollment, so the totals measure how many providers self-identify their primary practice as Internal Medicine Physician or Nephrology Physician rather than the total population ever trained or credentialed in either field, dual-certified clinicians show up under whichever code they registered first. Every figure is drawn from the federal National Provider Identifier Registry (CMS NPPES) - more than 7 million providers, maintained since May 2007, with 2023 Medicare Part D data, and, according to CMS, can be searched, compared, and traced in our methodology.

On national volume, Internal Medicine Physician carries the larger provider roster (172,737 vs 10,569), and Internal Medicine Physician has the wider geographic footprint at 56 states versus 55. The top Internal Medicine Physician concentration sits in California (20,046 providers), while Nephrology Physician peaks in California (1,150). The per-capita columns in the table below normalize each state's raw count against 2023 Census population estimates, which matters because absolute provider counts track population scale first and specialty density second, a small state with a strong training pipeline can out-rank a larger state on per-100K availability.

Use this comparison to understand relative availability, not to judge clinical substitutability - Internal Medicine Physician and Nephrology Physician are distinct specialties with different scopes of practice, training requirements, and conditions they treat, even when their NUCC categories overlap. Important: PlainDoctor is a directory of publicly available CMS government data, not medical advice, a provider rating, or a recommendation about which specialty a patient should consult. Always work with a licensed clinician to determine which specialty is appropriate for your condition, verify any specific provider through the NPPES NPI Registry and the relevant state medical board, and consult the NUCC taxonomy documentation for the formal scope-of-practice definitions behind each specialty code.