Type 1 · Individual ✓ Active NPI ✓ Valid NPI checksum Sole proprietor

William Norman Hamstra, D.O.

Surgery Physician in San Ramon, CA · enumerated 2005.

Data current as of Jul 13, 2026 · sourced from CMS NPPES

National Provider Identifier

1306835723

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Registry record

Entity type Individual (Type 1)

Name William Norman Hamstra

Credential D.O.

Sex Male

Practice address San Ramon, CA, 94583

Phone (925) 447-0660

Fax (925) 443-7506

Enumeration date Oct 18, 2005

Last updated in NPPES Feb 11, 2022

Street address withheld: NPPES sole-proprietor addresses can be home addresses. See our data policy.

Taxonomy & licenses

208600000X Surgery Physician Allopathic & Osteopathic Physicians · License 20A5413 (CA) Primary

DO · Doctor of Osteopathic Medicine: A fully licensed physician trained in osteopathic medical schools, with the same practice rights as an MD. About the DO credential

Other identifiers

Identifier	Type	State	Issuer
00AX54131	Medicaid	CA	-

What is an NPI number?

A National Provider Identifier (NPI) is a unique 10-digit number that CMS assigns to every U.S. healthcare provider and organization under HIPAA. Type 1 NPIs identify individual providers; Type 2 NPIs identify organizations. The NPI appears on insurance claims, prescriptions, and credentialing paperwork, and never changes, even if the provider moves or changes specialty.

Read the full guide → Validate an NPI →

Frequently asked questions

Where does William Hamstra practice?

The practice location on file with NPPES is in San Ramon, CA. Providers can have multiple locations; NPPES lists the primary practice address.

What is the NPI number for William Hamstra?

The National Provider Identifier (NPI) for William Hamstra is 1306835723, a Type 1 (individual) record in the CMS NPPES registry.

Other providers at this practice address

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Source: CMS NPPES (public data). Snapshot 2026-07-13. Provider record last updated 2022-02-11.