The CMS National Plan and Provider Enumeration System currently lists 271 Medical Oncology Physician providers with a primary practice address in California, all registered under the Internal Medicine NUCC taxonomy branch. Each clinician on this roster selected Medical Oncology Physician as their primary taxonomy at NPI enrollment, a self-reported classification that is updated whenever the provider files a correction with CMS. The count excludes organizations (group practices, hospitals, clinics operate under separate NPIs) and excludes providers who chose a different primary specialty even if they practice Medical Oncology Physician part-time. 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.

At 271 enrolled providers, Medical Oncology Physician in California is a limited-supply market, that matters for search-radius decisions, because patients in California outside the largest metros often need to broaden to adjacent cities to find a local Medical Oncology Physician clinician. The directory below is paginated 50 providers at a time (6 pages total) and is sorted alphabetically by last name, so scanning for a specific practice usually goes faster than scrolling; on the provider detail page you'll find the full NPPES record including address, phone, credentials, and any published Medicare Part D prescribing activity for 2023.

Before contacting anyone on this list, verify the practice is still at the address shown, NPPES refreshes monthly, but providers who have relocated, retired, or changed employers may not have filed an NPI update yet. Important: PlainDoctor is a directory of publicly available CMS government data covering Medical Oncology Physician providers in California, not a quality ranking, a board-certification verifier, or medical advice. Always confirm credentials through the NPPES NPI Registry, the California medical board, and, where relevant, the ABMS, AOA, or the specialty's primary certifying body before making any clinical decision. Nothing on this page substitutes for a conversation with a licensed clinician.