Quick answers
- Does William F. Johnston accept Medicare assignment?
- Yes. Medicare's clinician data says William F. Johnston accepts Medicare assignment (the Medicare-approved amount as full payment for covered services), as of October 2, 2026. Ask the office to confirm before your visit.
- How many Medicare patients does William F. Johnston see?
- In 2024, CMS data shows 43 Original Medicare patients and 56 services for William F. Johnston. This counts Original Medicare only and measures volume, not quality.
- What is William F. Johnston's NPI number?
- 1417366584. The NPI (National Provider Identifier) is the clinician's permanent federal ID; you can look it up in the official NPI Registry.
Medicare activity in 2024
Official CMS public-use data for William F. Johnston, data year 2024 (released May 21, 2026). It covers Original Medicare (fee-for-service) patients only, not Medicare Advantage or other insurance. It shows volume, not quality or outcomes. CMS hides any count of 10 or fewer patients.
| Original Medicare patients | 43 |
|---|---|
| Services billed to Medicare | 56 |
| Different services or procedures | 13 |
| Participating Medicare provider | Yes |
| Average age of these patients | 68 |
Most frequent services
- Emergency department visit with moderate level of medical decision making (99284)23 services
- Emergency department visit with high level of medical decision making (99285)12 services
Chronic conditions among these patients
Share of this clinician’s Original Medicare patients with each condition, as published by CMS (it describes the patients, not the care given).
- High blood pressure74%
- High cholesterol47%
- Diabetes35%
- Arthritis30%
- Depression28%
Hospitals where William F. Johnston works
Medicare's Facility Affiliation Data lists William F. Johnston at these hospitals (updated October 2, 2026). Each hospital page shows its address, phone, emergency services, Medicare rating and all its clinicians. Star rating and emergency services: Hospital General Information (CMS), data updated October 26, 2026.
- San Mateo Medical CenterSan Mateo, CA · Acute Care Hospital · Emergency services: listed by Medicare · CCN 050113
Practice locations
Addresses where William F. Johnston is enrolled with Medicare (CMS data updated October 2, 2026).
- 222 W 39th AveSan Mateo, CA 94403 (650) 573‑2222
Group practices
Medicare enrollment lists William F. Johnston as a member of this group (CMS data updated October 2, 2026).
- Cep America - California1,292 clinicians in the group
Specialties
- Emergency Medicineprimary
Other emergency medicine doctors in San Mateo
Clinicians with the same Medicare primary specialty in San Mateo, CA — not a recommendation.
Other clinicians in Cep America - California
Medicare enrollment lists these clinicians in the same group practice — not a recommendation.
Clinician information
| Credential | MD |
|---|---|
| Graduation year | 2013 (13 years since medical school) |
| Gender (as listed) | Male |
| Medicare assignment | Accepts (Medicare-approved amount as full payment) |
| NPI (National Provider Identifier) | 1417366584 |
| 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 October 2, 2026, retrieved October 29, 2026
- Hospital General Information — CMS, data updated October 26, 2026, retrieved November 13, 2026
- National Downloadable File (Doctors and Clinicians) — CMS, data updated October 2, 2026, retrieved October 29, 2026
- Medicare Physician & Other Practitioners - by Provider — CMS, data year 2024, released May 21, 2026; Medicare Physician & Other Practitioners - by Provider and Service
- 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