Quick answers
- Which hospitals does Denis Mahar work at?
- Medicare's official clinician data lists Denis Mahar at 3 hospitals: Contra Costa Regional Medical Center, John Muir Medical Center - Concord Campus and John Muir Medical Center - Walnut Creek Campus. This is where the clinician works or has privileges; call the hospital to confirm.
- Where does Denis Mahar see patients?
- Medicare's clinician data lists 1 practice location in Martinez, CA. Call before your visit to confirm the address.
- What is Denis Mahar's specialty?
- Medicare lists Internal Medicine as the primary specialty.
- Does Denis Mahar accept Medicare assignment?
- Medicare's clinician data says Denis Mahar may accept Medicare assignment (as of 2026-10-02). Ask the office whether they accept it for your visit.
- What is Denis Mahar's NPI number?
- 1841373891. The NPI (National Provider Identifier) is the clinician's permanent federal ID; you can look it up in the official NPI Registry.
Hospitals where Denis Mahar works
Medicare's Facility Affiliation Data lists Denis Mahar at these hospitals (updated 2026-10-02). Each hospital page shows its address, phone, emergency services, Medicare rating and all its clinicians.
- Contra Costa Regional Medical CenterMartinez, CA · Acute Care Hospital · CCN 050276
- John Muir Medical Center - Concord CampusConcord, CA · Acute Care Hospital · CCN 050496
- John Muir Medical Center - Walnut Creek CampusWalnut Creek, CA · Acute Care Hospital · CCN 050180
Practice locations
Addresses where Denis Mahar is enrolled with Medicare (CMS data updated 2026-10-02).
- 331 C StMartinez, CA 94553
Specialties
- Internal Medicineprimary
Other internal medicine doctors in Martinez
Clinicians with the same Medicare primary specialty in Martinez, CA — not a recommendation.
Clinician information
| Credential | MD |
|---|---|
| Medical school | Loyola University Of Chicago, Stritch School Of Medicine |
| Graduation year | 1992 |
| Gender (as listed) | Male |
| Medicare assignment | May accept for some services |
| NPI (National Provider Identifier) | 1841373891 |
| Corrections | Report an error or suggest an update → |
Most corrections must be made at the source: clinicians update their NPI Registry record (NPPES) and their Medicare enrollment (PECOS); this page follows the next data release.
Sources
- Facility Affiliation Data — Centers for Medicare & Medicaid Services (CMS), data updated 2026-10-02, retrieved 2026-10-29
- National Downloadable File (Doctors and Clinicians) — CMS, data updated 2026-10-02, retrieved 2026-10-29
- NPI Registry — U.S. Department of Health and Human Services (NPPES), the clinician’s official record
- Medicare Care Compare — official Medicare tool to look up clinicians