Quick answers
- Does William R. Mains accept Medicare assignment?
- Yes. Medicare's clinician data says William R. Mains 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 R. Mains see?
- In 2024, CMS data shows 18 Original Medicare patients and 105 services for William R. Mains. This counts Original Medicare only and measures volume, not quality.
- What is William R. Mains's NPI number?
- 1477751741. 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 R. Mains, 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 | 18 |
|---|---|
| Services billed to Medicare | 105 |
| Different services or procedures | 9 |
| Participating Medicare provider | Yes |
| Average age of these patients | 45 |
Most frequent services
- Residence visit for established patient with low level of medical decision making, per day, if using time, at least 30 minutes (99348)32 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).
- Anxiety75%
Practice locations
Addresses where William R. Mains is enrolled with Medicare (CMS data updated October 2, 2026).
- 1080 Marina Village Pkwy, Suite 100Alameda, CA 94501
Specialties
- Psychiatryprimary
Other psychiatrists in Alameda
Clinicians with the same Medicare primary specialty in Alameda, CA — not a recommendation.
Clinician information
| Credential | MD |
|---|---|
| Medical school | University Of California, San Diego School Of Medicine |
| Graduation year | 1996 (30 years since medical school) |
| Gender (as listed) | Male |
| Medicare assignment | Accepts (Medicare-approved amount as full payment) |
| Telehealth | Offers telehealth services |
| NPI (National Provider Identifier) | 1477751741 |
| 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
- 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