Internal Medicine Providers in Ontario, CA
Browse 9 Internal Medicine providers listed in NPPES with a practice address in Ontario, California.
How Ontario compares with the U.S.
9 active clinicians in Internal Medicine list a practice address in Ontario, CA in the NPI registry.
With fewer than 10 clinicians, rates per 100,000 residents are not reliable enough to compare.
Too few clinicians in Internal Medicine in Ontario are listed in the CMS Medicare file to report Medicare assignment or telehealth shares.
These figures summarize public federal data. They do not measure quality of care, appointment availability, or whether a clinician accepts your insurance or new patients. Registry addresses can be out of date. Please confirm details directly with the office and your plan. This information is not medical advice.
Prepared by T-MedInfo from NPPES, CMS and U.S. Census Bureau data. Questions or corrections: support@true-medinfo.com · Methodology
Sources: Clinician counts and practice addresses: NPPES NPI Registry, Centers for Medicare & Medicaid Services (CMS), data as of August 2026.
Dr. Liwanag Asuncion , MD
Internal Medicine
Dr. Dianne Elizabeth Quintana , MD
Internal Medicine
Dr. Yan Zhang , MD
Internal Medicine
Dr. David Herbert Daniels , MD
Internal Medicine
Sujay Dayal
Internal Medicine
Dr. Eric James Gureghian , MD
Internal Medicine
Dr. David Masao Hirota , MD
Internal Medicine
Dr. Rodman A St. Clair , MD
Internal Medicine
Dr. Kishan Thapar , MD
Internal Medicine
Frequently Asked Questions about Internal Medicine in Ontario
Each practitioner profile shows the NUCC taxonomy code and any state license number the practitioner reported to NPPES, plus a link to the California licensing board lookup. NPPES entries are self-reported; current license status is published only by the state board.
This list shows NPI records that are active in NPPES. A deactivated NPI keeps its profile with the deactivation date and practice history; find it with the site search by name or NPI number.
Other Specialties in Ontario
Internal Medicine Providers in Other California Cities
Cities with the most listed practitioners first.