Quick answers
- Which hospitals does Mariko Ishiyama work at?
- Medicare's official clinician data lists Mariko Ishiyama at 4 hospitals: Adventist Health Clearlake, Adventist Health St Helena, 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 Mariko Ishiyama see patients?
- Medicare's clinician data lists 3 practice locations, including Clearlake, CA, Concord, CA and Tulare, CA. Call before your visit to confirm the address.
- What is Mariko Ishiyama's specialty?
- Medicare lists Hospitalist as the primary specialty, and also Family Practice.
- Does Mariko Ishiyama accept Medicare assignment?
- Yes. Medicare's clinician data says Mariko Ishiyama accepts Medicare assignment (the Medicare-approved amount as full payment for covered services), as of 2026-10-02. Ask the office to confirm before your visit.
- What is the phone number for Mariko Ishiyama?
- (707) 994-6486, as listed in official Medicare / NPI Registry data.
- What is Mariko Ishiyama's NPI number?
- 1952662991. The NPI (National Provider Identifier) is the clinician's permanent federal ID; you can look it up in the official NPI Registry.
Hospitals where Mariko Ishiyama works
Medicare's Facility Affiliation Data lists Mariko Ishiyama at these hospitals (updated 2026-10-02). Each hospital page shows its address, phone, emergency services, Medicare rating and all its clinicians.
- Adventist Health ClearlakeClearlake, CA · Critical Access Hospital · CCN 051317
- Adventist Health St HelenaSaint Helena, CA · Acute Care Hospital · CCN 050013
- 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 Mariko Ishiyama is enrolled with Medicare (CMS data updated 2026-10-02).
- 15630 18th AveClearlake, CA 95422 (707) 994‑6486
- 2700 Grant St, Suite 200Concord, CA 94520 (925) 674‑0500
- 869 N Cherry StTulare, CA 93274 (559) 685‑3462
Group practices
Medicare enrollment lists Mariko Ishiyama as a member of these groups (CMS data updated 2026-10-02).
- Galen Inpatient Physicians PC1,077 clinicians in the group
- John Muir Physician Network494 clinicians in the group
Specialties
- Hospitalistprimary
- Family Practicealso
Other hospitalists in California
Clinicians with the same Medicare primary specialty in California — not a recommendation.
Clinician information
| Credential | DO |
|---|---|
| Graduation year | 2012 |
| Gender (as listed) | Female |
| Medicare assignment | Accepts (Medicare-approved amount as full payment) |
| NPI (National Provider Identifier) | 1952662991 |
| 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