This page compares two distinct NUCC-taxonomy specialties tracked by the CMS National Plan and Provider Enumeration System: Allergy & Immunology (Internal Medicine) Physician, which currently counts 517 enrolled providers across 47 U.S. states and territories, and Internal Medicine Physician, with 172,737 providers across 56 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 Allergy & Immunology (Internal Medicine) Physician or Internal Medicine 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 517), and Internal Medicine Physician has the wider geographic footprint at 56 states versus 47. The top Allergy & Immunology (Internal Medicine) Physician concentration sits in California (74 providers), while Internal Medicine Physician peaks in California (20,046). 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 - Allergy & Immunology (Internal Medicine) Physician and Internal Medicine 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.